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Question
Explain the term ‘variable valency’.
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Solution
“When an element has more than one valency, its valency is called variable valency.”
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Write the chemical formula of the following compound in a step-by-step manner –
Sodium bromide
Write the chemical formula of the following compound in a step-by-step manner –
Potassium sulphate
Write the chemical formula of the following compound in a step-by-step manner –
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Match the statements – 1 to 10 below with their correct answers from – A to J.
| Column I | Column II |
| 1. Elements having valency of two. | A: Br1− |
| 2. An anion | B: Divalent |
| 3. A gaseous non-metal | C: Reactants |
| 4. A cation. | D: Ammonium |
| 5. The term used for the substances which take part in the chemical reaction | E: Nitric oxide |
| 6. The meaning of the symbol ‘Δ’ over the arrow in a chemical equation. | F: Nitrogen |
| 7. The chemical name for nitrogen monoxide. | G: Zero |
| 8. A radical containing nitrogen and hydrogen only | H: Nitrous oxide |
| 9. The chemical name for dinitrogen oxide | I: Heat required |
| 10. The valency of noble gases | J: K1+ |
Match the compounds in List I – 1 to 20 with their correct formulas in List II – A to T.
| List I | List II |
| 1. Copper [I] sulphide | A: KMnO4 |
| 2. Potassium permanganate | B: Mg3N2 |
| 3. Phosphoric acid | C: Mg(NO3)2 |
| 4. Copper [I] oxide | D: Al2(SO4)3 |
| 5. Carbonic acid | E: Na2ZnO2 |
| 6. Aluminium sulphide | F: N2O |
| 7. Iron [II] oxide | G: H2CO3 |
| 8. Iron [III] sulphide | H: Al2S3 |
| 9. Iron [II] sulphate | I: NO |
| 10. Sodium zincate | J: FeS |
| 11. Nitrous oxide | K: Fe2S3 |
| 12. Aluminium sulphate | L: H3PO4 |
| 13. Magnesium nitride | M: Cu2S |
| 14. Iron [III] sulphate | N: CuS |
| 15. Copper [II] oxide | O: Fe2O3 |
| 16. Iron [III] oxide | P: FeO |
| 17. Nitric oxide | Q: FeSO4 |
| 18. Copper [II] sulphide | R: Fe2(SO4)3 |
| 19. Iron [II] sulphide | S: CuO |
| 20. Magnesium nitrate | T: Cu2O |
