Why has `D_(2)O` more density than `H_(2)O`

Why is N_(2)O_(5) more acidic than N_(2)O_(3) ?

Why is O_(3) more reactive than O_(2) ?

H_(2)S is. more acidic than H_(2)O because

Why H_(2) is more stable than H_(2)^(+) while He_(2)^(+) is more stable than He_(2) ?

D_O is more polar than H_2O.

Statement-I: Polarity of H_(2)O_(2) is more than H_(2)O but it is a fewer solvent than H_(2)O . Statement-II: In chemical reactions, H_(2)O is decomposed but H_(2)O does not.

D_(2)O is used more in

Statement-1: H_(2)O_(2) is more polar than H_(2)O Statement-2: D_(2)O has higher boiling point than H_(2)O Statement-3: H_(2) bond bond energy is less than D_(2) .