If heat is supplied to an ideal gas in an isothermal process,a) the internal energy of the gas will increaseb) the gas will do positive workc) the gas will do negative workd) the said process is not possible.

the ans is that the gas will do positive work. according to us it will be negative.

the work will be done because the energy, in form of heat, supplied will not change the temperature (being isothermal), so the energy needs to be cancelled out. therefore gas will do the required work. for us, it is negative, by convention, but it is positive for the gas.