The chemical symbol for nitrogen gas is

The molecule having an atomicity of $4$ is

Which of the following correctly represents $360 \, g$ of water?
$(i)$ $2$ moles of $H_2O$
$(ii)$ $20$ moles of water
$(iii)$ $6.022 \times 10^{23}$ molecules of water
$(iv)$ $1.2044 \times 10^{25}$ molecules of water

Give two examples to show that the law of conservation of mass applies to physical changes also.

Find the total number of atoms present in one $SO_{4}^{2-}$ ion.

State whether the following statement is true or false:
Iron shows valencies of $Fe^{2+}$ and $Fe^{3+}$.