Ans 2:
Class : Class 8
Yes there are 6 combinations but if you check some of them are same like -CB and MB , MB and CBSo there will be only three combinations
Ans 6:
Class : Class 7
The six different combinations are CB and NB,CB and MB,NB and CB,NB and MB,MB and CB and finally Mb and CB. But CB and NB and NB and CB are same, same with NB,MB and MB,NB and CB,MB and MB,CB...Thus there are only 3 unique options available...
Ans 7:
Class : Class 7
if you check you will get 3 combinations, because the question says that the two bars taken are not of the same type.