Question

why is the formula of cyclopentane is C5H10 it should be C5H12 as per the alkane formula

Answer 1

There are three types
1- C5H12 (Alkane)
2- C5H10 (Alkene)
3- C5H8 (Alkyne)

These are 3 different compounds formed different formulae

Answer 2

Cyclopentane is in cyclic structure. They have one saturated hydrogen ring
Their general formula is CnH2n
not CnH2n+2