Chemistry Grade 12

Chemistry Past Papers 12th Class Gujranwala Board

Section A-(MCQs)

i) The newspaper can be recycled again as many time as:                (Mark 1)

A. 5
B. 3
C. 4
D. 2
A. 5

Section B-(Short Questions)

Q.2 i) "Ionization energy increases from left to right in a period.” Justify the statement.                                                                                                            (Marks 2)

As we move from left to right in a period, the outer shell remains the same, while the nuclear charge increases effectively that makes the removal of an electron difficult and hence the value of ionization energy increases.

Section C-(Long Questions)

Q.5 a) Discuss the position of hydrogen over VII A-Group elements.
                                                                                                                                            (Marks 4)

Position of Hydrogen over VII A-Group Elements
Hydrogen has certain similarities with halogens due to this it can be placed above VII A-group elements.
But it also shows certain differences with this group. Therefore, it is difficult to decide its position in the periodic table.

  • Hydrogen is a gas like most of halogens.

  • Hydrogen exists in diatomic form (H2) like F2, Cl2, and I2.

  • Hydrogen requires one electron to complete its outermost shell just like halogens.

  • Both hydrogen and halogens form stable ionic compounds with alkali metals.

  • Hydrogen forms H- ion by gaining one electron like F-, Cl-, Br-, etc.


  • Hydride ion H- is unstable in aqueous solution while halides ions, i.e,. F-, Cl-, Br- etc, are stable.
    H-    +    H2O   →    H2   +   OH-

  • Hydrogen has just one electron in its outermost shell while halogens have seven electrons in their outermost shells.

  • Hydrogen forms very stable compound H2O with oxygen while halogens do not form.

  • Alkali metal hydrides e.g. NaH are mostly basic while alkali metals halides e.g. NaCl are neutral.

  • Hydrogen can form H+ ion by losing an electron, while halogens do not form positive ions.

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