The total internal energy U of a monoatomic ideal gas is given by:
[tex]U=\frac{3}{2}nRT[/tex]Where n is the amount of substance, R is the universal gas constant and T is the temperature of the sample. The value of R is:
[tex]R=8.314\frac{J}{mol\cdot K}[/tex]Replace n=1.3mol and T=315K to find the internal energy of the gas:
[tex]U=\frac{3}{2}(1.3mol)\left(8.314\frac{J}{mol\cdot K}\right)(315K)=5106.87...J[/tex]Therefore, the approximate total internal energy of the gas is 5100J. The correct choice is Option B.