A sample of pure Cu (3.18g ) heated in a stream of oxygen for some time gains in mass with the formation of black oxide of copper (CuO). The final mass is 3.92 g. The percent of copper remains unoxidised is-

1.$\approx$6.5 

2.$\approx$6.9

3. $\approx$7.6

4. $\approx$7.9

One mole of a mixture of CO and CO₂ requires exactly 20g of NaOH in solution for the complete conversion of all the CO₂ into Na₂CO₃. How much NaOH would it require for conversion into Na₂CO₃, if the mixture (one mole) is completely oxidised to CO₂?

1. 60g

2. 80g

3. 40g

4. 20g

The mass  of 50% (w/w) solution of HCl required to react with 100g of CaCO₃ would be:

(1) 73g

(2) 100g

(3) 146g

(4) 200g

Versene, a chelating agent having chemical formula C₂H₄N₂(C₂H₂O₂Na)₄. If each mole of this compound could bind 1 mole of Ca²⁺, then the rating of pure versene expressed as mg of CaCO₃ bound per g of chelating agent is:

1. 100 mg

2. 163 mg

3. 200 mg

4. 263 mg

A gas is found to have the formula (CO)_x. Its VD is 70. The value of x must be:

1. 7 

2. 4

3. 5

4. 6

When 100 mL of PH₃ is decomposed, it produces phosphorus and hydrogen. The change in volume is:

The molality of 1M solution of NaCl ( specific gravity 1.0585 g/mL ) is:

1. 1.0585

2. 1.0

3. 0.10

4. 0.0585

The total molarity of all the ions present in  0.1 M of CuSO₄ and 0.1 M of Al₂(SO₄)₃ solution is:

1. 0.2M

2. 0.7M

3. 0.8M

4. 1.2M

A solution contains Na₂CO₃ and NaHCO₃. 10 mL of the solution required 2.5 mL of 0.1 M H₂SO₄ for neutralisation using phenolphthalein as indicator. Methyl orange is then added when a further 2.5 mL of 0.2 M H₂SO₄ was required. The amount of Na₂CO₃ and NaHCO₃ in 1 litre of the solution is:

1. 5.3g and 4.2g

2. 3.3g and 6.2g

3. 4.2g and 5.3g

4. 6.2g and 3.3g

Equal volumes of 0.1 M AgNO₃ and 0.2 M NaCl are mixed. The concentration of N${\mathrm{O}}_3^{-}$ ions in the mixture will be: