NTSE Stage 2 SAT 2019 Exam Question Paper

Question : 74 of 100

Marks: +1, -0

Read the following statements.
Statement I: Sodium metal reacts violently with water to produce heat and fire.
Statement II: Potassium metal reacts violently with water to form potassium hydroxide and hydrogen gas.
Select the correct answer from the options given below.

Statement I is true, Statement II is false.
Statement I is false, Statement II is true.
Both Statements are true and Statement n provides explanation to Statement I.
Both Statements are true but Statement II does not provides explanation to Statement I.

Validate

Solution:

Sodium metal reacts violently with water because it is much more active than hydrogen. When sodium is put into water, the de-localised electrons flow into the water leaving the positive ions to remain. The positive ions strongly repel each other and this repulsion causes the metal to explode.

2Na(s)+H_2O(l)→2KOH+H_2(g)+\text "Heat energy"

Metals lime Na, K, Ca, Mg etc. react with water to produce metal oxide and hydrogen gas. Sodium and potassium reacts violently with cold water and evolve hydrogen, which immediately catches fire.

2K(s)+H_2O(l)→2KOH+H_2(g)+\text "Heat energy"

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