The correct statement amongst the following is :

Options

1. AThe term 'standard state' implies that the temperature is $0^{\circ} \mathrm{C}$
2. BThe standard state of pure gas is the pure gas at a pressure of 1 bar and temperature 273 K
3. C$\Delta_{\mathrm{f}} \mathrm{H}_{298}^\theta$ is zero for $\mathrm{O}(\mathrm{g})$
4. D$\Delta_{\mathrm{f}} \mathrm{H}_{500}^\theta$ is zero for $\mathrm{O}_2(\mathrm{~g})$