Isothermal compression leaves Kp unchanged and mole fractions initially unaltered

Steps:

• Recognize that Kp depends solely on temperature; constant T means Kp unchanged.
• Note compression decreases volume, raising total pressure proportionally for all gases.
• Understand mole fraction of Z is moles Z divided by total moles, unaffected immediately by volume change.
• Conclude no shift in composition is implied without specifying re-equilibration time, so no change in mole fraction.

Why B is correct:

• Kp is defined as a function of temperature only (van't Hoff equation), and mole fractions depend on relative moles, which don't alter instantly upon compression.

Why the others are wrong:

• A: Kp cannot increase at constant T.
• C: Mole fraction of Z cannot decrease; compression favors no immediate drop.
• D: Identical to B, so not distinct.

Final answer: B