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ICSE Class 10 Chemistry Question 2 of 10

Analytical Chemistry — Question 9

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Question 9

Assertion (A): Oxides of most of the metals are basic in nature.

Reason (R): All metal oxides dissolve in water forming alkalis.

  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false but R is true.
Answer

A is true but R is false.

Explanation — Oxides of most of the metals are basic in nature. They dissolve in water forming hydroxides (or alkalis).

For example:

Na2Osodium oxide+H2O⟶2NaOHsodium hydroxide\underset{\text{sodium oxide}}{{\text{Na}_2\text{O}}} + \text{H}_2\text{O} \longrightarrow \underset{\text{sodium hydroxide}}{2\text{NaOH}}

Hence the assertion (A) is true.

Reason (R) is false because, not all metal oxides dissolve in water to form alkalis. A few metallic oxides and hydroxides exhibit dual character, i.e., they show acidic as well as basic character. They are said to be amphoteric in nature.
For example : Copper(II) oxide (CuO)

CuO + H2O ⟶ No reaction