The correct order of the following compounds showing increasing tendency towards nucleophilic substitution reaction is :

The incorrect statement among the following is :

In polymer Buna-S : 'S' stands for :

Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R.

Assertion A : Hydrogen is the most abundant element in the Universe, but it is not the most abundant gas in the troposphere.

Reason R : Hydrogen is the lightest element.

In the light of the above statements, choose the correct answer from the options given below :