(i) At constant temperature, the **pressure ***p *and **volume ***V* of a gas are** inversely proportional**; *pV = *constant; graph of isothermal pressure/volume curves. (iii) At constant pressure, the **volume ***V *of a gas is **directly proportional **to its **temperature ***T *(in **Kelvin**); *V/T = *constant; graph. (iii) At constant volume, the **pressure ***p* of a gas is **directly proportional **to its **temperature ***T *(in **Kelvin**); *p/T *= constant; graph.