Natural numbers:
The natural numbers are the positive integers (whole numbers) starting from 1.
[tex]\N=\mleft\lbrace1,2,3,4,5\ldots\mright\rbrace[/tex]
Note that natural numbers are never negative or fraction/decimal.
Let us analyze the given options and identify the natural numbers.
1st option: √32
This is an irrational number and hence not a natural number,
2nd option: 4/28
As you can see this is not a whole number since it is in fraction.
Therefore, it is not a natural number.
3rd option: -√49
As you can see it is a negative integer and we know that natural numbers are never negative.
Therefore, it is not a natural number.
4th option: √81
Notice that the square root of 81 is 9 that is a positive integer. (whole number)
[tex]\sqrt[]{81}=9[/tex]
Therefore, it is a natural number.
5th option: 28/4
Notice that 28/4 can be simplified to 7 that is a positive integer (whole number)
Therefore, it is a natural number.
6th option: -15
As you can see it is a negative integer and we know that natural numbers are never negative.
Therefore, it is not a natural number.
Hence, only 4th and 5th options are natural numbers.
