A sample of ammonia gas, NH3, has a volume of 285.0 mL at a pressure of 98.50 kPa. What will the volume of the ammonia be at a pressure of 94.20 kPa? Assume that all other properties of the gas remain constant.

Using Avogadro's law

where: P1V1/n1T1 = P2V2/n2T2

The problem states it implicitly but n and T are constant

P1V1 = P2V2

V2 = P1V1/P2

P1 = 98.50 kPa

V1 = 285.0 mL

P2 = 94.20 kPa

V2 = (98.50 x 285) / 94.20

V2 = 298.00 mL

The volume increases to 298 mL.

We know that an ideal gas keeps the relation between pressure, volume and temperature constant.

P * V / T = constant

Then if we have the gas in two diferente state:

P1*V1/T1 = P2*V2/T2

Temperature remain constant so then:

P1*V1 = P2*V2

98.5*285 = 94.2*V2

V2 = 98.5*285/94.2 = 298 ml

So the volume of the ammonia will be 298 ml