a b c d

b

$\text{Velocity of A after collision }V_A = \frac{v}{3}$ $\text{Velocity of B after collision }V_B = \frac{4v}{3}$ $ \frac{\lambda_A}{\lambda_B} = \frac{m_B}{m_A} \times \frac{V_B}{V_A} = \frac{1}{2} \times \frac{4}{1} = 2$