If Avogadro number \(N_{A}\), is changed from$\mathrm{}$ \(6 . 022 \times \left(10\right)^{23}\)\(\text{mol}^{- 1}\) to \(6 . 022 \times \left(10\right)^{20} ~\text{mol}^{- 1}\) this would change the:

20.0 g of a magnesium carbonate sample decomposes on heating to give carbon dioxide and 8.0 g of magnesium oxide.
The percentage purity of magnesium carbonate in the sample is: 
(Atomic weight of Mg=24)

What is the mass of the precipitate formed when 50 mL of 16.9% solution of AgNO₃ is mixed with 50 mL of 5.8% NaCl solution? (Ag = 107.8, N = 14, O = 16, Na= 23, Cl = 35.5)
1. 28 g
2. 3.5 g
3. 7 g
4. 14 g

Calculate the mole fraction of the solute in a 1.00 m aqueous solution.

A mixture of gases contains H₂ and O₂ gases in the ratio of 1 : 4 (w/w). The molar ratio of the two gases in the mixture will be:

When 22.4 litres of H₂(g) is mixed with 11.2 litres of Cl₂(g), both at STP, the moles of HCl(g) formed are equal to:

1. 1 mol of HCl(g)
2. 2 mol of HCl(g)
3. 0.5 mol of HCl(g)
4. 1.5 mol of HCl(g)

1.0 g of magnesium is burnt with 0.56 g O₂ in a closed vessel. Which reactant is left in excess and by how much? (At. wt. Mg = 24; O = 16)