UPSC Civil Services 2016 Prelims General Studies Paper II

By looking at all the options, we observe that option (b) is not necessarily true.
We know that, a number is divisible by 10 iff it has 0 at the unit's place.
(R+S) may or may not have 0 at the unit's place. Therefore, it may or may not be divisible by 10 .
Thus, it is not necessarily true.