I have paid municipal taxes on my house pertaining to the year 2017-18 in April 2018. Can I claim deduction of such taxes for FY 2017-18 (AY 2018-19)?

Where the municipal taxes have become due but not been actually paid, the same will not be allowed. Municipal taxes are always allowed as a deduction only on payment basis.

Though you have paid taxes pertaining to FY 2017-18, since the payment has been made in April 2018 i.e. FY 2018-19, it will be allowed for FY 2018-19 only as a deduction from Gross Annual Value.