Question

if a gas is heated at constant pressure,what happens to its isothermal compressibility

Answer 1

isothermal means constant temperature

Answer 2

at constant pressure,the gas will expand on heating as Volume is directly proportional to Temperature at constant pressure.
as the gas will expand the the gas particles will get far away from each other and repulssive forces between them will dominate.the particles will be more scattered across the volume and hence the empty volume available in the gas for compression will be less.
After heating to a certain temp. and then keeping it constant,its isothermal compressibility will decrease as the volume has increased than the initial volume,so it will be less compressible then.

Answer 3

harder.