Correct option is (c) 2.21 m/s
Let mass of each ball be 'm'.
By conservation of energy for system AB
Ki + Ui = Kf + Uf
0 + mg(2r) = \(\frac12\)(m + m)v2 + 0
mg x 2(0.25) = \(\frac12\) x 2mv2
g x 0.5 = v2
10 x 0.5 = v2
\(\frac{10}2\) = v2
v = √5 m/s
v = 2.21 m/s