Question

no. if moles = given mass!/molecular mass........ ....
so it should be unitless quantity
then why it is expressed in 'mol'

Answer 1

No of moles is a unitless quantity.
'mol' is used to express the terms in which the numerical value is entered.
For eg: if you have 10 apples and lose 5, how many do you have left? 5 apples. Here, "apples" isn't a unit, it's describing the amount i.e. 5.

Same way, when we have 1 mole of a substance, it indicates that the substance is taken in moles.