Answer
b) B's half-life is 3 times that of A.
Work Step by Step
Given: $\lambda_{A}=3\lambda_{B}$
Half-life of B=$\frac{0.693}{\lambda_{B}}$
Half-life of A=$\frac{0.693}{\lambda_{A}}=\frac{0.693}{3\lambda_{B}}=\frac{1}{3}\times \text{half-life of B}$
$\implies \text{half-life of B}=3\times\text{half-life of A}$
