A gas mixture consists of 8 moles of argon and 6 moles of oxygen at...

As we know, internal energy is given by, $U = n{C}_{v}T$. Also argon gas is monoatomic and oxygen gas is diatomic.

Therefore, total internal energy will be${U}_{net} = {n}_{1}{C}_{{V}_{1}}T + {n}_{2}{C}_{{V}_{2}}T$

$= 8 \times \dfrac{3R}{2} \times T + 6 \times \dfrac{5R}{2} \times T$

$= 27RT$