Answer: The partial pressure of Helium is 400 mm Hg.
Explanation:
According to Dalton's law, the total pressure is the sum of individual pressures of all the gases present in the system.
[tex]p_{total}=p_1+p_2[/tex]
[tex]p_{total}=p_{N_2}+p_{O_2}+p_{He}[/tex]
given :
[tex]p_{total}=760mmHg[/tex]
[tex]p_{N_2}=90mmHg[/tex],
[tex]p_{O_2}=270mmHg[/tex]
Putting in the values we get:
[tex]760mmHg=90mmHg+270mmHg+p_{He}[/tex]
[tex]p_{He}=400mmHg[/tex]
Thus the partial pressure of Helium is 400 mm Hg.