Sir,

sorry it is little bit confusing. "GATE FORUM Engineering Success" replies this question the correct is option (C) with explanation as given below :

Exp: L_{1 }: {a^{m}b^{n}a^{n}b^{m} }This one is CFL

L_{2} : {a^{m}b^{n}a^{m}b^{n} } by pumping lemma this one is not CFL.

L_{3} : {a^{m}b^{n} } ;m = 2n +1 This is CFL.

Where as your above explanation show correct option is (B) which contradicts each other. please explain. so that the readers may be able to understand the correct answer.