Correct Answer - A::B
Let `theta` be the desired angle. Linear momentum of the system will remain conserved.
Hence, `p^2=p_1^2+p_2^2+2p_2p_2costheta`
or `{2m(v/2)}^2=(mv)^2+(mv)^2+2(mv)(mv)costheta`
or `1=1+1+2costheta` or `costheta=-1/2`
`:. theta=120^@`