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

The atomic numbers of three elements $A, B$ and $C$ are $9, 10$ and $13$ respectively. Which of them will form a cation?

The mass of one steel screw is $4.11 \, g$. Find the mass of one mole of these steel screws. Compare this value with the mass of the Earth $(5.98 \times 10^{24} \, kg)$. Which one of the two is heavier and by how many times?

Calculate the number of atoms in $120 \, g$ of calcium and $120 \, g$ of iron. Which one has more number of atoms and what is the difference? (Given: atomic mass of calcium $= 40 \, u$ and iron $= 56 \, u$)

State the postulate of Dalton's atomic theory which led to the law of conservation of mass. Calculate the molecular mass of water.

$A$ chlorine atom is electrically neutral,but a chloride ion is a charged ion. Explain.