Answer :
We are given that the total pressure in the vessel is
$$P_{\text{total}} = 750\, \text{kPa},$$
with the partial pressures of neon and argon being
$$P_{\text{Ne}} = 230\, \text{kPa} \quad \text{and} \quad P_{\text{Ar}} = 250\, \text{kPa}.$$
Since the gases are part of a mixture, the sum of the partial pressures of all gases equals the total pressure. Let the partial pressure of helium be $P_{\text{He}}$. Then, we have:
$$
P_{\text{total}} = P_{\text{Ne}} + P_{\text{Ar}} + P_{\text{He}}.
$$
Substitute the known values:
$$
750 = 230 + 250 + P_{\text{He}}.
$$
First calculate the sum of the neon and argon pressures:
$$
230 + 250 = 480.
$$
Now, subtract this sum from the total pressure to find the helium pressure:
$$
P_{\text{He}} = 750 - 480 = 270\, \text{kPa}.
$$
Thus, the partial pressure of helium is $270\, \text{kPa}$.
The correct answer is option B.
$$P_{\text{total}} = 750\, \text{kPa},$$
with the partial pressures of neon and argon being
$$P_{\text{Ne}} = 230\, \text{kPa} \quad \text{and} \quad P_{\text{Ar}} = 250\, \text{kPa}.$$
Since the gases are part of a mixture, the sum of the partial pressures of all gases equals the total pressure. Let the partial pressure of helium be $P_{\text{He}}$. Then, we have:
$$
P_{\text{total}} = P_{\text{Ne}} + P_{\text{Ar}} + P_{\text{He}}.
$$
Substitute the known values:
$$
750 = 230 + 250 + P_{\text{He}}.
$$
First calculate the sum of the neon and argon pressures:
$$
230 + 250 = 480.
$$
Now, subtract this sum from the total pressure to find the helium pressure:
$$
P_{\text{He}} = 750 - 480 = 270\, \text{kPa}.
$$
Thus, the partial pressure of helium is $270\, \text{kPa}$.
The correct answer is option B.
