What is the concentration of a urea solution if 6.02×10²⁰ molecules of urea are present in 100 mL of the solution?

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

Find the minimum molecular weight of the enzyme peroxidase anhydrase
 if it contains 0.5% selenium by weight.
(Atomic weight of Se = 78.4)

1. 1.568 x 10⁴ 

2. 15.68

3. 2.168 x 10⁴ 

4. 1.568 x 10³ 


 

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