Concentrated nitric acid is 70% HNO₃. The amount of concentrated nitric acid solution that should be used to prepare 250 mL of 2.0 M HNO₃ would be:

1. 90.0 g conc. HNO₃
2. 70.0 g conc. HNO₃
3. 54.0 g conc. HNO₃
4. 45.0 g conc. HNO₃

The mole fraction of the solute in a 1.00 molal aqueous solution is: 

6.02x10²⁰ molecules of urea are present in 100mL of its solution. The concentration of the solution is:

Which of The following has a maximum number of molecules?

1. 7g N₂ 

2. 2g H₂ 

3. 16g NO₂ 

4. 16g O₂ 

Calculate the number of moles of oxygen in 1L of air containing 21% oxygen by volume, under standard conditions.

1. 0.0093 mole

2. 2.10 moles

3. 0.186 mole

4. 0.21 mole

How much oxygen gas (O₂) at standard temperature (0°C) and pressure (1 atm) is required to completely combust 1 liter of propane gas (C₃H₈) under the same conditions?

1. 7L 
2. 6L
3. 5L
4. 10L

1 g of magnesium is burnt with 0.56g of oxygen in a closed vessel. The left-out reactant and its quantity are

(At. weight of Mg = 24, O=16)

Percentage of Se in peroxidase anhydrase enzyme is 0.5% by weight (at. weight = 78.4), then minimum molecular weight of peroxidase anhydrase enzyme is

1. 1.568 x 10³ 

2. 15.68

3. 2.168 x 10⁴ 

4. 1.568 x 10⁴ 

Assuming fully decomposed, the volume of CO₂ released at STP on heating 9.85g of BaCO₃ [at. mass of Ba = 137] will be

1. 1.12L

2. 0.84L

3. 2.24L

4. 4.96L

The total number of valence electrons in 4.2g of ${\mathrm{N}}_3^{-}$ ion is (N_A is the Avogadro's number)

1. 2.1N_A 

2. 4.2N_A 

3. 1.6N_A 

4. 3.2N_A