Dear swapnil ,
there is a method of solving objective questions called solving by elimination. although we can try about solving for Sn -Sn-1 but in case of objective exams where speed matters it is better to use the former one.
so here , Sn -Sn-1 = an , i.e. nth term.
a) apply n=2 , we get a2 not equal to 22 so the option is eliminated.
b) not clearly mentioned by you.
c)apply two a2 is 22 but it you shud check also for n =9 where it gives wrong answer so option is eliminated.
d) manually see it is right .
so option d is correct.
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