Available Answers

1. 1.

   Name or state with reference to hydrogen - the first element of the periodic table.

   	Name/state
   1. The period of the periodic table to which the element hydrogen belongs.
   2. The two subgroups of the periodic table in which hydrogen can be placed.
   3. The element in period-3 which is electropositive and shows similarity to hydrogen.
   4. The number of valency electrons in hydrogen.
   5. An element in period-2 which has the same atomicity as hydrogen.
   6. An element which combines with both hydrogen and halogens forming covalent compounds.
   7. An electrovalent compound formed from an element in period-3 and hydrogen.
   8. A covalent gaseous compound formed from an element in period-3 and hydrogen.
   9. A covalent gaseous compound formed from an element in group 14 [IVA] and hydrogen.
   10. An oxide of hydrogen which is neutral in nature.
   11. The number of shared pairs of electrons in a diatomic molecule of hydrogen.
   12. A non-metallic element in period-1, group-1 [IA] of the periodic table.
   13. The element in period-3 which is electro negative and shows similarity to hydrogen.

    

2. 2.

   Complete the following sentences by filling in the blanks with the appropriate word/s.

   1. The first element hydrogen of the periodic table shows similarity with ______________ metals of group 1 [IA] and ______________ of group 17 [VIIA].
   2. Hydrogen shows electropositive character. Elements in group 1 [IA] are considered electropositive since they have a tendency to ______________ one electron from its valence shell.
   3. Hydrogen also shows electronegative character. Elements in group 17 [VIIA] are considered electronegative since they have a tendency to ______________ one electron forming an electronegative element.
   4. The electronic configuration of the element in period-3 which has the same number of valence electrons as hydrogen is ______________.
   5. The element in group 1 [IA] which has one electron less than the noble gas present in period-1 of the periodic table is ______________.
   6. Hydrogen is a diatomic molecule which has two atoms linked by a ______________ covalent bond. The element in group 17 [VIIA] which is also diatomic and exists in the liquid state at room temperature is ______________.
   7. Halides of hydrogen and alkali metals yield ______________ ions in aqueous solution. During electrolysis these ions are discharged at the negative electrode i.e. cathode.
3. 3.

   Hydrogen can be positioned in group 1 [IA] and group 17 [VIIA] of the periodic table. Give reasons.

4. 4.

   Hydrogen can be represented as H¹⁺ or as H^1-. Give reasons.

5. 5.

   Match the points pertaining to the occurrence and discovery of hydrogen - in Column I with the concluding facts in Column II.

   COLUMN I	COLUMN II
   A. Lavoisier in 1783 established the name 'hydrogen'	1. the atmosphere around the sun and stars.
   B. Hydrogen does not occur	2. water
   C. Hydrogen is present in traces in	3. meaning 'water producer'
   D. A compound, one ninth by mass of which is hydrogen in the combined state is	4. in the free state on earth.

    

6. 6.

   Hydrogen is prepared from - cold water, boiling water or steam by reaction with certain metals involving - potassium, sodium, calcium, magnesium, aluminium, zinc, iron. Complete & balance the equations for the reactions of the above metals - with water by substituting the correct symbols in each case.

   1. Reaction with cold water
      1. X + H₂O → XOH + H₂ [X-burns in air with a lilac flame]
      2. Y + H₂O → YOH + H₂ [Y-burns in air with a golden yellow flame]
      3. Z + H₂O → Z(OH)₂ + H₂ [Z - burns in air with a brick red flame]
   2. Reaction with boiling water or steam
      1. Q + H₂O → QO + H₂ [QO - is a basic oxide]
      2. R + H₂O → RO + H₂ [RO - is an amphoteric oxide]
      3. S + H₂O → S₂O₃ + H₂ [S - is a trivalent metal]
      4. T + H₂O ⇄ T₃O₄ + H₂ [Reaction of T with steam is reversible]