Number with HCF 1 with 9.

**The reasoning** HCF (Highest Common Factor) means the largest number that divides both numbers perfectly. For two numbers to have HCF = 1, they must be **coprime** — sharing no common factors except 1. Let's check what divides 9: only 1, 3, and 9. - **A) 3**: Factors are 1, 3. Both 3 and 9 share 3 as a factor → HCF = 3 ❌ - **B) 5**: Factors are 1, 5. Only 1 divides both 5 and 9 → HCF = 1 ✓ - **C) 6**: Factors are 1, 2, 3, 6. Both 6 and 9 share 3 → HCF = 3 ❌ - **D) 12**: Factors are 1, 2, 3, 4, 6, 12. Both 12 and 9 share 3 → HCF = 3 ❌ **Why the wrong options tempt you** All the wrong answers (3, 6, 12) are multiples of 3 or contain 3 as a factor — and since 9 = 3², they all share 3 as a common divisor. If you don't carefully check the factors, these look innocent enough to pick. **Quick takeaway** To have HCF = 1 with 9, pick a number that doesn't have 3 as a factor — because 9 is built entirely from 3s!