Assertion (A) : 1 + 3 + 5 + 7 + ……. + 21 = 10².

Reason (R) : The sum of first n odd natural numbers = n².

1. Both A and R are correct, and R is the correct explanation for A.

2. Both A and R are correct, and R is not the correct explanation for A.

3. A is true, but R is false.

4. A is false, but R is true.

Express 21² as the sum of two consecutive whole numbers.

Is 336 a perfect square ? If not, find the smallest multiple of 336 which is a perfect square.

Find the least number that must be subtracted from 980 so as to get a perfect square. Also, find the square root of the perfect number obtained.