Observation

In part (a), the question did not require the candidates to carry out actual test. Majority of the candidates were able to name gas M, identify J and K, but failed to name N as retort stand and clamp.

In part (b), majority of the candidates could not give the confirmatory test for gas M, and state the method of collecting it.
In part (c), only few candidates could write the balanced equation of reaction for the preparation of gas M.
In part (d), majority of the candidates could not state the defect in the diagram for the preparation of gas M.

Expected answer include:

3(a)     

J          -           Thistle funnel             
K        -           U – tube                     
L         -           Fused Calcium chloride / Anhydrous calcium chloride
M        -           Hydrogen gas
N         -           Retort stand and clamp

(b)

(i)         To dry the H2 gas / acting as a drying agent
(ii)        Upward delivery (of gas) / downward displacement of air  
(iii)       Introduce burning splintin the gas, pop sound produced      

(c)        Zn(s) + 2HCl(aq)  →   ZnCl2(aq) + H2(g)   
           
(d)      

-           U-tube is hanging in air.
-           No clamp holding the conical flask to the retort stand