If Avogadro number ${\mathrm{N}}_{\mathrm{A}}$, is changed from $6.022\times {10}^{23}$ $mo{l}^{-1}$ to $6.022\times {10}^{20}$ $mo{l}^{-1}$ this would change:

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 will be: 
(Atomic weight of Mg=24)

What is the mass of 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.

1. 0.177
2. 0.771
3. 0.0534
4. 0.0177

The number of water molecules is maximum in?
1. 18 molecules of water
2. 1.8 g of water
3. 18 g of water
4. 18 moles of water

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 is 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)
1. Mg, 0.16 g
2. $O_2$, 0.16 g
3. Mg, 0.44 g
4. $O_2$, 0.28 g