[JNW2]

119. A gaseous material XY(g) dissociates to some extent to pro- duce X(g) and Y(g):
XY(g) <--> X(g) + Y(g)

A 2.00-g sample of XY (molar mass =165 g/mol) is placed in a container with a movable piston at 25 C. The pressure is held constant at 0.967 atm. As XY begins to dissociate, the piston moves until 35.0 mole percent of the original XY has dissociated and then remains at a constant position. Assuming ideal behavior, calculate the density of the gas in the container after the piston has stopped moving, and determine the value of K for this reaction of 25 C.

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Attempt to solve the problem:
I think to use the law of ideal gas
PV =nRT and use Kp =K(RT)^ (delta n)

[AWK]

Where is density in your formulas?
When unspecified K - it may be Kc or Kp (easier calculations)