diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..d621040b2 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -12,4 +12,9 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
+// console.log(`My house number is ${address[0]}`);
+
+// The original syntax works for array and not for object.
+// it will show undefine message
+// Instead use the correct . operator to access the object field values
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..50447e4ff 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -11,6 +11,14 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
+// for (const value of author) {
+//  console.log(value);
+// }
+
+for (const key in author) {
+  console.log(author[key]);
 }
+
+// the iteration method does not work for the object.
+// TypeError TypeError: author is not iterable will be shown
+// Change the correct method with the object
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..e279a0145 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -10,6 +10,14 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+//console.log(`${recipe.title} serves ${recipe.serves}
+//  ingredients:
+//${recipe}`);
+
+for (const ingredient of recipe.ingredients) {
+  console.log(ingredient);
+}
+
+
+// [object Object] will be shown because JavaScript converts an object to a string, it becomes "[object object].
+// Use the syntax to access the ingredients directly 
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..4f8354667 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,13 @@
-function contains() {}
+function contains() {
+
+    // Return false if obj is null, undefined, an array, or not a non-null object
+    if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+        return false;
+    }
+
+    // Check if the property exists directly on the object
+    return Object.prototype.hasOwnProperty.call(obj, prop);
+  
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..2daa43068 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -17,19 +17,33 @@ as the object doesn't contains a key of 'c'
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
 
-// Given an empty object
-// When passed to contains
-// Then it should return false
-test.todo("contains on empty object returns false");
-
-// Given an object with properties
-// When passed to contains with an existing property name
-// Then it should return true
-
-// Given an object with properties
-// When passed to contains with a non-existent property name
-// Then it should return false
-
-// Given invalid parameters like an array
-// When passed to contains
-// Then it should return false or throw an error
+    // Given an empty object
+    // When passed to contains
+    // Then it should return false
+    test("contains on empty object returns false", () => {
+        expect(contains({}, "a")).toBe(false);
+    });
+
+    // Given an object with properties
+    // When passed to contains with an existing property name
+    // Then it should return true
+    test("returns true when passed an existing property name", () => {
+        const inputObj = { a: 1, b: 2 };
+        expect(contains(inputObj, "a")).toBe(true);
+        expect(contains(inputObj, "b")).toBe(true);      
+    });
+
+    // Given an object with properties
+    // When passed to contains with a non-existent property name
+    // Then it should return false
+    test("returns false when passed a non-existent property name", () => {
+        const inputObj = { a: 1, b: 2 };
+        expect(contains(inputObj, "c")).toBe(false);
+    });
+
+    // Given invalid parameters like an array
+    // When passed to contains
+    // Then it should return false or throw an error
+    test("returns false when passed invalid parameters like arrays or primitives", () => {
+        expect(contains([1, 2, 3], "0")).toBe(false);
+    });
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..63ed72807 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,4 +1,8 @@
 function createLookup() {
+
+    return Object.fromEntries(countryCurrencyPairs);  
+  
+  
   // implementation here
 }
 
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..e2f8f1801 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,35 +1,20 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
-/*
-
-Create a lookup object of key value pairs from an array of code pairs
-
-Acceptance Criteria:
-
-Given
- - An array of arrays representing country code and currency code pairs
-   e.g. [['US', 'USD'], ['CA', 'CAD']]
-
-When
- - createLookup function is called with the country-currency array as an argument
-
-Then
- - It should return an object where:
- - The keys are the country codes
- - The values are the corresponding currency codes
-
-Example
-Given: [['US', 'USD'], ['CA', 'CAD']]
-
-When
-createLookup(countryCurrencyPairs) is called
-
-Then
-It should return:
- {
-   'US': 'USD',
-   'CA': 'CAD'
- }
-*/
+test("creates a country currency code lookup for multiple codes", () => {
+    // Given
+    const input = [
+        ["US", "USD"],
+        ["CA", "CAD"],
+    ];
+
+    const expectedOutput = {
+        US: "USD",
+        CA: "CAD",
+    };
+
+    // When
+    const result = createLookup(input);
+
+    // Then
+    expect(result).toEqual(expectedOutput);
+});
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..7bf291348 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,13 +1,50 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+  
+  if (!queryString || queryString.length === 0) {
     return queryParams;
   }
+
+  // Helper to decode '+' as spaces and percent-encoded characters
+  function decodeParam(str) {
+    return decodeURIComponent(str.replace(/\+/g, " "));
+  }
+
+  // Split by '&' to get raw key-value pairs
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    // Ignore empty pairs caused by trailing or duplicate '&' (e.g. "a=1&&b=2&")
+    if (pair.length === 0) {
+      continue;
+    }
+
+    let rawKey, rawValue;
+    const equalIndex = pair.indexOf("=");
+
+    if (equalIndex === -1) {
+      // Key with no '=' (e.g., "key") -> value is empty string
+      rawKey = pair;
+      rawValue = "";
+    } else {
+      // Split on the FIRST '=' only (handles values containing '=', e.g. "a=b-2")
+      rawKey = pair.slice(0, equalIndex);
+      rawValue = pair.slice(equalIndex + 1);
+    }
+
+    const key = decodeParam(rawKey);
+    const value = decodeParam(rawValue);
+
+    // Stretch Goal: Handle duplicate keys by converting to an array
+    if (Object.prototype.hasOwnProperty.call(queryParams, key)) {
+      if (Array.isArray(queryParams[key])) {
+        queryParams[key].push(value);
+      } else {
+        queryParams[key] = [queryParams[key], value];
+      }
+    } else {
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 328b8df61..962ecf8a7 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -38,6 +38,12 @@ test("should replace '+' by ' '", () => {
 });
 
 // Stretch exercise: Handling query strings that contain identical keys
+test("should handle multiple duplicate keys alongside single keys", () => {
+    expect(parseQueryString("tag=js&tag=node&author=CYF")).toEqual({
+        tag: ["js", "node"],
+        author: "CYF",
+    });
+});
 
 // Delete this test if you are not working on this optional case
 test("should store values of a key in an array when the key has 2 or more values", () => {
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..16c800576 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,12 @@
-function tally() {}
+function tally(items) {
+    if (!Array.isArray(items)) {
+        throw new TypeError("Expected an array as input");
+    }
+
+    return items.reduce((acc, item) => {
+        acc[item] = (acc[item] || 0) + 1;
+        return acc;
+    }, {});
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..ced8a644e 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -19,16 +19,30 @@ const tally = require("./tally.js");
 // Given a function called tally
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
+test("returns counts for each unique item", () => {
+    expect(tally(["a"])).toEqual({ a: 1 });
+    expect(tally(["a", "b", "c"])).toEqual({ a: 1, b: 1, c: 1 });
+  });
 
 // Given an empty array
 // When passed to tally
 // Then it should return an empty object
-test.todo("tally on an empty array returns an empty object");
+test("tally on an empty array returns an empty object", () => {
+    expect(tally([])).toEqual({});
+  });
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("returns counts for each unique item", () => {
+    expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+    expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+  });
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("throws an error when passed an invalid input like a string", () => {
+    expect(() => tally("string")).toThrow(TypeError);
+    expect(() => tally("string")).toThrow("Expected an array as input");
+  });
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..1780b9993 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -17,13 +17,29 @@ function invert(obj) {
 }
 
 // a) What is the current return value when invert is called with { a : 1 }
-
+{ key: 1 }
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
-
+{ key: 2 }
 // c) What is the target return value when invert is called with {a : 1, b: 2}
-
+{ "1": "a", "2": "b" }
 // c) What does Object.entries return? Why is it needed in this program?
-
+Object.entries(obj) returns an array of key-value pairs as two-element arrays.
+Object.entries({ a: 1, b: 2 }) returns [["a", 1], ["b", 2]].
 // d) Explain why the current return value is different from the target output
-
+The line invertedObj.key = value; contains bugs:
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+function invert(obj) {
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    throw new TypeError("Expected a plain object");
+  }
+
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+
+module.exports = invert;
diff --git a/Sprint-2/stretch/count-words.js b/Sprint-2/stretch/count-words.js
index 8e85d19d7..811033859 100644
--- a/Sprint-2/stretch/count-words.js
+++ b/Sprint-2/stretch/count-words.js
@@ -26,3 +26,27 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+function countWords(str) {
+  if (typeof str !== "string") {
+    throw new TypeError("Expected a string as input");
+  }
+
+  // Handle empty or whitespace-only strings
+  if (str.trim() === "") return {};
+
+  const words = str.split(" ");
+  const counts = {};
+
+  for (const word of words) {
+    if (counts[word]) {
+      counts[word] += 1;
+    } else {
+      counts[word] = 1;
+    }
+  }
+
+  return counts;
+}
+
+module.exports = countWords;
diff --git a/Sprint-2/stretch/mode.js b/Sprint-2/stretch/mode.js
index 3f7609d79..b7bc5138b 100644
--- a/Sprint-2/stretch/mode.js
+++ b/Sprint-2/stretch/mode.js
@@ -8,6 +8,7 @@
 // refactor calculateMode by splitting up the code
 // into smaller functions using the stages above
 
+/*
 function calculateMode(list) {
   // track frequency of each value
   let freqs = new Map();
@@ -34,3 +35,43 @@ function calculateMode(list) {
 }
 
 module.exports = calculateMode;
+*/
+
+function getFrequencies(list) {
+  const freqs = new Map();
+
+  for (const num of list) {
+    if (typeof num !== "number") {
+      continue;
+    }
+    freqs.set(num, (freqs.get(num) || 0) + 1);
+  }
+
+  return freqs;
+}
+
+
+function getHighestFrequencyKey(freqs) {
+  let maxFreq = 0;
+  let mode;
+
+  for (const [num, freq] of freqs) {
+    if (freq > maxFreq) {
+      mode = num;
+      maxFreq = freq;
+    }
+  }
+
+  return maxFreq === 0 ? NaN : mode;
+}
+
+function calculateMode(list) {
+  const freqs = getFrequencies(list);
+  return getHighestFrequencyKey(freqs);
+}
+
+module.exports = {
+  calculateMode,
+  getFrequencies,
+  getHighestFrequencyKey,
+};
diff --git a/Sprint-2/stretch/till.js b/Sprint-2/stretch/till.js
index 6a08532e7..d52e37433 100644
--- a/Sprint-2/stretch/till.js
+++ b/Sprint-2/stretch/till.js
@@ -23,9 +23,41 @@ const till = {
 const totalAmount = totalTill(till);
 
 // a) What is the target output when totalTill is called with the till object
-
+"£4.40"
 // b) Why do we need to use Object.entries inside the for...of loop in this function?
-
+We need it because plain objects are not directly iterable using a for...of loop in JavaScript. Using Object.entries allows us to loop through the entries
 // c) What does coin * quantity evaluate to inside the for...of loop?
-
+coin * quantity evaluates to NaN (Not-a-Number).
 // d) Write a test for this function to check it works and then fix the implementation of totalTill
+  function totalTill(till) {
+  let totalPence = 0;
+
+  for (const [coin, quantity] of Object.entries(till)) {
+    // Parse the numeric pence value from strings like "50p" -> 50
+    const penceValue = parseInt(coin, 10);
+    
+    if (!isNaN(penceValue)) {
+      totalPence += penceValue * quantity;
+    }
+  }
+
+  // Convert pence to pounds and format to 2 decimal places
+  const pounds = (totalPence / 100).toFixed(2);
+  return `£${pounds}`;
+}
+
+module.exports = totalTill;
+
+const totalTill = require("./totalTill.js");
+
+describe("totalTill", () => {
+  test("calculates the correct total for a given till object", () => {
+    const till = {
+      "1p": 10,
+      "5p": 6,
+      "50p": 4,
+      "20p": 10,
+    };
+    expect(totalTill(till)).toBe("£4.40");
+  });
+});