The HCF of the first five odd natural numbers is:

The correct answer is Option (4) → 1

The HCF (highest common factor) of a set of numbers is the largest number that divides every one of them.

• The first five odd natural numbers are 1, 3, 5, 7 and 9

• The only factor of 1 is 1 itself, so no number larger than 1 can divide all five

• HCF \(=\) 1

Even without the 1, the HCF would still be 1: 3, 5 and 7 are different primes with no common factor other than 1.