since no2 is meta directing will the electrophile and nucleophile always attack the meta position of benzene in presence of nitro grp(provided it is not hindered)

Satyaprakash, One half of your question is almost correct while the other half is factually incorrect. Let us analyse it as follows:-

1) Electrophilic substitution:- Now, the NO2 group is electron withdrawing grp which withdraws the electron density away from the ring through the strong -R effect and also the weaker -I effect. The effect of this electron withdrawing is observed more at the Ortho- and Para- positions as they are involved in resonance delocalisation whereas the Meta- position does not take part in resonance delocalisation and hence, the electron density is not withdrawn from it and has more electron density than that of o- and p- positions. Now, electrophile is electron deficient and it attacks an electron rich site which is meta- in this case, so the attack takes place at m- position to give meta- substituted product except in a few cases where the steric and other factors dominate. The deciding factor is the stability of the sigma- complex formed on the attack of an electrophile.

2) Nucleophilic substitution:- Similar to the above situation, the electron density is withdrawn more from the ortho- and para- positions( from the NO2 group whereas no such effect is observed at meta- position. So, electron density is lower at o- and p- positions and since nucleophile is an electron rich specie, therefore it attacks electron deficient sites which are ortho- and para- positions to give corresponding o- and p- substituted products. Therefore, in this case of nucleophilic subn, the major product is o- and p- substituted derivates.