The set of counting numbers starting with 1 and continuing 2,3,4.....and so on are called Natural Numbers.

Product of any two whole numbers is always a Whole Number.
For eg: If we multiply two numbers say 5 and 7, $5\times 7=35$, 35 is also a whole number.

Natural numbers are counting numbers. The natural numbers start with 1. So 1 is the smallest number possible in natural numbers.

If you divide something by 2 you divide that thing into 2 parts. If you divide something by 4 you divide that thing into 4 parts. Now if you divide something by 0, you cannot divide that thing into 0 parts. So a division by 0 is undefined and Rahul is correct.

Using distributive property

12 times 35 = 12 times (20+15)

The difference between two consecutive numbers is 1 and let's consider this difference to be a one step.
The cat is at number 3 and the rat is at number 10. The difference between 10 and 3 is 7, therefore the rat is 7 steps away from the cat.

4, when represented as four dots, can result in a line, rectangle and a square.

Every square is a rectangle.

The number of whole numbers between any two numbers
=  (the difference between the numbers) -1.
The difference between 9900 - 9876 is 24 and 24 -1 = 23.

So, there are 23 whole numbers are there between 9876 and 9900.

Yes it is correct.

9 can be written as 10 - 1

So 117 + 9 = 117 + 10 - 1

Again (117+ 10) = 127, so (117+ 10) - 1 = 127 - 1 

Associative Property states: When three or more numbers are added, the sum is the same regardless of the order of addition. The property states that for all real numbers a, b, and c, their sum is always the same, regardless of their grouping. (a+b)+c = a+ (b+c)

So (267 + 345) + 21 and 267 + (345 + 21) will give the same result = 633.