Hello,

             Coming to your question there is a chance for getting a job in these 3 of the offices...

1. ONGC---there is good scope in it but its like allowed only up to staff level. The exam you need to clear is GATE and then followed by interview...

2. ISRO----- to get into isro you need to clear ICRB exam.

3. BARC----actually in this there are 2 ways firstly is that u can enter into by taking up research scholar exam which is a written exam that is conducted in February every year and the cutoff mark in this exam is 155/300 

Second method is through GATE exam and it must be a merit list and the cutoff is 840/1000

Coming to pay scale it varies at different levels so we can't judge exactly

All the best........