Question 1

The question was attempted by majority of the candidates and the performance was good.

In part (a)(i), candidates correctly gave name and corresponding nature of the radiations emitted during radioactivity as follows:

- alpha particle, (doubly charged) helium nucleus/high ionizing/low penetrating power/deflected towards negative plate
- beta particle, (fast moving) electron/moderate ionizing/moderate penetrating power/deflected towards positive plate
- gamma radiation, (high energy) electromagnetic radiation/low ionizing/high penetrating power/no effect on magnetic field.

Some candidates however lost marks because of spelling mistakes and use of symbols to denote the particles (i.e alfa for alpha or a instead of alpha).

In part (a)(ii), only very few candidates were able to give corresponding differences between chemical reaction and nuclear reaction as follows:

Chemical reaction		Nuclear reaction
- atoms are rearranged by the	-	elements are converted to other
breaking and forming of chemical		elements/new elements may be
bond/no new atom is		formed/atomic number or mass
formed/atomic number or mass		number of each element may change.
number of each element does not
change
- only (valence) electrons are involved.		- protons, neutrons, electrons and other elementary parties may be involved.
- reactions are accompanied by absorption/release of (relatively) small amount of energy.		- reactions are accompanied by release of (relatively) large amount of energy.
- rate of reaction is influenced by temperature, pressure, concentration and catalyst.		- rate of reaction normally are not affected by pressure, temperature and catalyst.

In(a)(iii), most candidates correctly balanced the nuclear reactions and identify X and Y thus:

     (iii)               ²¹²₈₄PO → ²⁰⁸₈₂Pb +⁴₂ X                    X is α- particle/helium nucleus I⁴₂He

                  ¹³⁷₅₅Cs → ¹³⁷₅₆Ba + ⁰_-1Y                           Y is β - particle/electron    ⁰_-1e

In part (b) (i) - (v), majority of the candidates correctly answered as follows:
(i)            atomic number - 17
(ii)           group 7
(iii)           - formation of diatomic molecules
                 - formation of monovalent ions/same valence electrons
                 - they are coloured substances
                 - they are oxidizing agents
                 - most electronegative in its period/smallest atomic size in its period
                 - they are non metals
(iv)         chlorine (formula was not accepted)
(v)          3Cl₂ + 6NaOH   →   5NaCl + NaCl0₃ + 3H₂0
However, some of the candidates lost marks because they could not give a correct balanced equation for the reaction of element X and hot concentrated NaOH.

In part (c )(i), most candidates lost marks because they did not know that graphite was used as a lubricant because of its planar layers which slides over each other and that diamond has three dimensional network which makes it so hard hence, used as a cutting tool in I and II respectively.

In part (c)(ii), candidates correctly wrote the reaction equation thus:

 

Also the gave the name of the reaction as combination/neutralization in (iii).