Question

One mole of a gas mixture is heated under constant pressure

Answer 1

your question is incomplete. A complete question is -----> One mole of an ideal gas is heated under constant pressure from 0°C to 100°C then work done will be

from law of thermodynamics,
at constant pressure, workdone = nR∆T
where n is no of mole of gas, R is universal gas constant and ∆T is change in temperature.

given,
n = 1mol , R = 25/3 J/mol/K and ∆T = (100°C - 0°C) = 100°C or, 100K

now, workdone = 1 × 25/3 × 100
= 2500/3 J
= 833.33 J