Answer
a) 1-isopropylcyclobutane (Molecular formula: $C_{6}H_{12}$)
b) 1-tertbutyl-3-methylcyclopentane (Molecular formula: $C_{10}H_{20}$)
c) 1,3-dimethyl-2-propylcyclohexane (Molecular formula: $C_{11}H_{22}$)
Work Step by Step
a) Count the ring carbons. here, it is 4. hence, root name is 'but' and 'cyclo' is added before 'but'. Now, one substituent namely isopropyl group is present at C1 position. So, add '1-isopropyl' before 'cyclobut' and ending name is 'ane' for alkane.
b) count the ring carbons. Here, it is 5. hence, root name is 'pent' and 'cyclo' is added before 'pent'. Now, one methyl group and one tertbutyl group are present at C3 and C1 position respectively. so, '1-tertbutyl-3-methyl' is added before root name. Ending name is 'ane' for alkane.
c) count the ring carbons. Here, it is 6. hence root name is 'cyclohex' and ending name is 'ane'. now, look out for the substituents present. Here, one two methyl groups and one propyl groups are present at C1,C3 and C2 positions respectively. So, '1,3-dimethyl-2-propyl' is added before root name.
For finding out the molecular formula of the compounds, we have to count the total no. of C atoms present in the compound. If total no. of C atoms = n, then total no. of H will be = 2n. Because general formula for cycloalkane is $C_{n}H_{2n}$
