The partial pressure of a gas is the pressure that the gas would exert if it were the only gas present in the container.
The partial pressure of a gas can be calculated using the following formula:
$$P_i=P_T\cdot X_i$$
Where:
* $$P_i$$ is the partial pressure of the gas in atm,
* $$P_T$$ is the total pressure of the mixture in atm,
* $$X_i$$ is the mole fraction of the gas in the mixture.
The mole fraction of a gas is the ratio of the number of moles of that gas to the total number of moles of gas in the mixture.
In this problem, we have a mixture of 0.220 moles CO, 0.350 moles H2, and 0.640 moles He with a total pressure of 2.95 atm.
We can calculate the mole fraction of H2 using the following formula:
$$X_{H_2}=\frac{0.350\text{ mol}}{0.220\text{ mol}+0.350\text{ mol}+0.640\text{ mol}}=0.259$$
We can then use the mole fraction of H2 to calculate the partial pressure of H2 using the following formula:
$$P_{H_2}=2.95\text{ atm}\times0.259=\boxed{0.765\text{ atm}}$$
Therefore, the partial pressure of H2 in the mixture is 0.765 atm.
