Assertion : Compressibility factor for hydrogen varies with pressure with positive slope at all pressures.Reason : Even at low pressures, repulsive forces dominate hydrogen gas.

For Hydrogen ($H_2$), the compressibility factor $Z$ increases with pressure, showing a positive slope even at $273\text{K}$. This indicates that $H_2$ is more difficult to compress than an ideal gas. The reason is that repulsive forces dominate in Hydrogen gas across all observed pressures. Both statements are true and the reason explains the assertion.