CE Chemistry V

Q.1
Most metal oxides do not react with water. Only the metal oxides of some (not all) very reactive metals in Group I and Group II (e.g. Na2O, K2O, CaO and BaO) can react with water to form solutions of metal hydroxides.

The commonest example is the reaction between CaO and water to give Ca(OH)2­ solution.
CaO(s) + H2O(l) → Ca(OH)2(aq)

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Q.2
NH4+ and OH- ions can only exist in aqueous solutions, but cannot exist as a stable compound.

When the solvent a solution containing NH4+ and OH- ions is evaporated (even at a low temperature), NH4+ and OH- would be decomposed to give NH3 gas and water.
NH4+(aq) + OH-(aq) → NH3(g) + H2O(l)

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Q.3
In a molecule of organic acid, only the H atom in the -COOH group is ionization, because -COO- can stably exist in water.

On the other hand, all H atoms are NOT ionization, because the C-H bonds are strong. Besides, if ionization occurs in C-H bonds, the -C- anion is formed which is very unstable.

some organic acid is polybasic, such as ethanedioic acid, which is dibasic.
But you only have to remember that only the H bonded to a COO group can ionized, because the COO- formed in losing a H+ is very stable (due to delocalization of electron and the electron withdrawing C=O group).