(a) 48
$960 = 2^6 \times 3 \times 5$; $432 = 2^4 \times 3^3$. HCF = $2^4 \times 3 = 48$.
Use prime factorisation: HCF = product of the smallest powers of common prime factors. Both share $2^4$ and $3^1$, giving $16 \times 3 = 48$. Always write the factorisation step in board exams for full credit.