The number of moles of a gas is propotional to it's partial pressure.
Increase in partial pressure of BrCl=0.46atm
from the given equilibrium constant,
Br
2+Cl
2 2BrCl can be derived.
therefore decrease in partial pressures of Cl
2 and Br
2=0.23atm (as one mole of Cl
2 and Br
2 produces two moles of BrCl)
new partial pressure of Cl
2=0.51atm-0.23atm=0.28atm
new partial pressure of Br
2=0.34atm-0.23atm=0.11atm