Graduate Pharmacy Aptitude Test (GPAT) 2012 Solved Paper

Some of the following statements describe the properties of Dropping Mercury Electrode (DME) correctly:
[P] Constant renewal of electrode surface eliminates poisoning effects.
[Q] Mercury makes many metal ions easily reducible.
[R] Mercury has large hydrogen over-voltage.
[S] The electrode can get oxidised with ease.
Identify the correct combination.