The correct option is A is true but R is false
Explanation
Oxidation is defined as the gain of oxygen or the loss of electrons by a substance during a chemical reaction. The nature of the resulting oxide (acidic or basic) depends on whether the element reacting with oxygen is a metal or a non-metal. Generally, metal oxides are basic in nature, whereas non-metal oxides are acidic.
Statement-wise Analysis
- Assertion (A): Correct. When magnesium burns in air, it reacts with oxygen to form magnesium oxide ($2Mg + O_2 \rightarrow 2MgO$). Since magnesium gains oxygen in this process, it is said to be oxidised.
- Reason (R): Incorrect. Magnesium is a metal, and magnesium oxide ($MgO$) is a metallic oxide. Metallic oxides are basic in nature. When dissolved in water (moisture), magnesium oxide forms magnesium hydroxide [$Mg(OH)_2$], which is a base. Bases turn red litmus paper blue. They do not turn blue litmus paper red; that is a property of acids.
Key Takeaway: Oxidation involves the addition of oxygen. Metal oxides are basic and turn red litmus blue, while non-metal oxides are acidic and turn blue litmus red.