Answer :

Correct answer is : 800

For the column whose one end fixed and another end free :

Buckling load P₁ = 100 N, L₁ = 2L

If the free end is replaced by pinned joint L₂ = $\frac{L}{\sqrt{2}}$

Since the column is the same $P_e\propto \frac{1}{L_e^2}$

$\frac{P_2}{P_1}=\frac{L_1^2}{L_2^2}$

P₂ = $100\times \frac{4L^2}{\frac{L^2}{2}}$ = 800 N