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

How many grams of concentrated nitric acid solution should be used to prepare 250 mL of 2.0 M HNO₃? The concentrated acid is 70% HNO₃.

Which has the maximum number of molecules among the following ?

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)