(c) $Y = \frac{\frac{F}{A}}{\frac{l}{L}} = \frac{F \times L}{A \times l}$
(where Y is Young’s modulus of elasticity Since, Y, L and A remain same.
$F \propto l$
$\frac{F_{1}}{F_{2}} = \frac{l_{1}}{l_{2}}$
⟹ $\frac{F}{F_{2}} = \frac{2 \times 10^{- 3}}{4 \times 10^{- 3}}$
$F_{2} = 2F$