diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..59669c771 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -13,3 +13,23 @@ const address = {
 };
 
 console.log(`My house number is ${address[0]}`);
+
+//my prediction is "undefined" because objects use names. When we js executes this code it is seeing address[0], it looks
+//for 0 in objects, won't find it and will return , undefined. 
+
+// i have run the code in devtools and got the "My house number is undefined" message.
+
+//the fixed code 
+
+const address = {
+  houseNumber: 42,
+  street: "Imaginary Road",
+  city: "Manchester",
+  country: "England",
+  postcode: "XYZ 123",
+};
+
+console.log(`My house number is ${address.houseNumber}`);
+
+
+
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..33d9273f7 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -14,3 +14,19 @@ const author = {
 for (const value of author) {
   console.log(value);
 }
+
+// this code will throw an error because on line for 14 it is trying to loop a plain object. 
+
+const author = {
+  firstName: "Zadie",
+  lastName: "Smith",
+  occupation: "writer",
+  age: 40,
+  alive: true,
+};
+
+for (const value of Object.values(author)) {
+  console.log(value);
+}
+
+//we fix this by using Object.values, i.e. turning plain object in an array. 
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..933ae093e 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -13,3 +13,19 @@ const recipe = {
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
 ${recipe}`);
+
+//Prediction:  
+//output will be, [object Object]. Because recipe is an object, when js converts objects to a string (template literals can only insert strings) it calls on toString() method, which 
+//by default returns [Object Object]. We can fix this code by using join(\n) method. 
+
+//fixed code:
+
+const recipe = {
+  title: "bruschetta",
+  serves: 2,
+  ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
+};
+
+console.log(`${recipe.title} serves ${recipe.serves}
+Ingredients:
+${recipe.ingredients.join("\n")}`);
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..f8d9f79ee 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,9 @@
-function contains() {}
+function contains(obj, property) {
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    return false;
+  }
+
+  return Object.hasOwn(obj, property);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..0097d8d69 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -17,19 +17,47 @@ 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
 
+test("returns true if the object contains the property", () => {
+  const object = { a: 1, b: 2 };
+
+  expect(contains(object, "a")).toBe(true);
+});
+
+test("returns false if the object does not contain the property", () => {
+  const object = { a: 1, b: 2 };
+
+  expect(contains(object, "c")).toBe(false);
+});
+
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns 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 property exists", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).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 property does not exist", () => {
+  expect(contains({ a: 1, b: 2 }, "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 for an array", () => {
+  expect(contains(["a", "b"], "0")).toBe(false);
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..da5b177d4 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,11 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  const lookup = {};
+
+  for (const [countryCode, currencyCode] of countryCurrencyPairs) {
+    lookup[countryCode] = currencyCode;
+  }
+
+  return lookup;
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..a8ad2bbd2 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,6 +1,19 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
+test("creates a country currency code lookup for multiple codes", () => {
+  const countryCurrencyPairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+    ["GB", "GBP"],
+  ];
+  const result = createLookup(countryCurrencyPairs);
+ 
+  expect(result).toEqual({
+    US: "USD",
+    CA: "CAD",
+    GB: "GBP",
+  });
+});
 
 /*
 
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..32daa79af 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,13 +1,43 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+
+  if (queryString === "") {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+ 
+    if (pair === "") continue;
+
+   
+    const equalsIndex = pair.indexOf("=");
+
+    let key, value;
+
+    if (equalsIndex === -1) {
+      key = pair;
+      value = "";
+    } else {
+      key = pair.slice(0, equalsIndex);
+      value = pair.slice(equalsIndex + 1);
+    }
+
+    
+    key = decodeURIComponent(key.replace(/\+/g, " "));
+    value = decodeURIComponent(value.replace(/\+/g, " "));
+
+    
+    if (queryParams.hasOwnProperty(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..8f2ce6823 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -37,12 +37,23 @@ test("should replace '+' by ' '", () => {
   });
 });
 
-// Stretch exercise: Handling query strings that contain identical keys
+test("returns empty object for empty query", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("ignores multiple empty pairs", () => {
+  expect(parseQueryString("&&&&")).toEqual({});
+});
 
-// 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", () => {
-  expect(parseQueryString("key=value1&key=value2&key=value3&foo=bar")).toEqual({
-    key: ["value1", "value2", "value3"],
-    foo: "bar",
+test("decodes encoded spaces", () => {
+  expect(parseQueryString("name=John%20Doe")).toEqual({
+    name: "John Doe",
   });
 });
+
+test("keeps all '=' in values", () => {
+  expect(parseQueryString("expr=a=b=c=d")).toEqual({
+    expr: "a=b=c=d",
+  });
+});
+
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..68af13a7a 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,19 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("Input must be an array");
+  }
+
+  const counts = {};
+
+  for (const item of items) {
+    if (counts[item]) {
+      counts[item]++;
+    } else {
+      counts[item] = 1;
+    }
+  }
+
+  return counts;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..403b3fdd1 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -20,15 +20,40 @@ const tally = require("./tally.js");
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
 
+test("returns an object containing the count for each unique item", () => {
+  expect(tally([1, 2, 2, 3, 3, 3])).toEqual({
+    1: 1,
+    2: 2,
+    3: 3,
+  });
+});
+
 // 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("counts duplicate items", () => {
+  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 for invalid input", () => {
+  expect(() => tally("abc")).toThrow();
+});
+
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..853ae6a9f 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -18,12 +18,61 @@ 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() returns an array of an object's key-value pairs, and it is needed in this program
+//so the for...of loop can access both each key and its corresponding value to swap them.
+
 // d) Explain why the current return value is different from the target output
 
+//It is different because invertObj.key creates a property literally calley "key". If we want to use the value of 
+//a variable as the property name, (invertedObj[value] = key) must be used instead.
+
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+function invert(obj) {
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+
+
+
+describe("invert", () => {
+  test("inverts an empty object", () => {
+    expect(invert({})).toEqual({});
+  });
+
+  test("inverts a single property", () => {
+    expect(invert({ a: 1 })).toEqual({ 1: "a" });
+  });
+
+  test("inverts multiple properties", () => {
+    expect(invert({ a: 1, b: 2 })).toEqual({
+      1: "a",
+      2: "b",
+    });
+  });
+
+  test("works with other values", () => {
+    expect(invert({ x: 10, y: 20 })).toEqual({
+      10: "x",
+      20: "y",
+    });
+  });
+});
+