Did I post it in wrong section of forum????

no you post it in the right section.

two conditions are there

1) it should be the bigest  party or group among the opposition

2) the group/ party have to get at least 10/15/20 % of the total seats of perliament or legislature.

( 10/15/20 %  -  i am not sure about it  )

The leader of single largest oppostion party which is having minimum 10% strenght of house is eligible to become 'Leader of Opposition'. If no party has 10% strenght of house, two or more parties having aggregate strenght of 10% of house may elect any MLA to be their leader; and that leader could be declared as 'Leader of Opposition' by the Speaker of House.