6.02 $$ \times $$ 10²⁰ molecules of urea present in 100 mL of its solution. The concentration of solution is

Which has the maximum number of molecules among the following ?

The number of atoms in 0.1 mol of a triatomic gas is (N_A = 6.02 $$ \times $$ 10²³ mol^$$-$$1)

25.3 g of sodium carbonate, Na₂CO₃ is dissolved in enough water to make 250 mL of solution. If sodium carbonate dissociates completely, molar concentration of sodium ion, Na⁺ and carbonate ions, CO$${}_3^{2 - }$$ are respectively (Molar mass of Na₂CO₃ = 106 g mol^$$-$$1)