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ICSE Class 9 Chemistry Question 29 of 34

The Language of Chemistry — Question 22

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22
Question

Question 2(vi)

Assertion (A): Magnesium phosphate is written as Mg3(PO4)2.

Reason (R): The valencies of magnesium and phosphate are three and two respectively.

  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 — The molecular formula of Magnesium phosphate is Mg3(PO4)2. Hence, the given assertion (A) is true.

Given the formula Mg3(PO4)2 :

Mg3(PO4)2=Mg23 ↗↖ PO42⇒Mg32 ↗↖ PO43\text{Mg}_3(\text{PO}_4)_2 = \underset{\phantom{2}{3}}{\text{Mg}} \space {\nearrow}\mathllap{\nwarrow} \space \underset{2}{\text{PO}_4} \Rightarrow \overset{\phantom{3}{2}}{\text{Mg}} \space {\nearrow}\mathllap{\nwarrow} \space \overset{3}{\text{PO}_4} \\[0.5em]

∴ Valency of magnesium (Mg) is 2 and Phosphate is 3. Hence, the reason (R) is false.