Look at the table of srp values below.

In this case we only care about the copper and the hydrogen half reactions listed in the table. Both reactions are written as reduction reactions (gaining electrons) and the SRP (standard reduction potential) is listed on the right. In this case, copper ions have a higher reduction potential (+0.34V) in comparison to hydrogen (0.00V) so the copper ion reduction reaction in the table will be favoured in the cell.

In redox voltaic cells, oxidation (losing electrons) occurs at the ANODE, and reduction (gain electrons) occurs at the CATHODE.

To work out the final reaction, we reverse the unfavourable reduction half reaction so it becomes an oxidation reaction to produce a redox reaction, and we leave the favourable reduction half reaction as it is. So in this case, copper ions will be reduced to elemental copper at the CATHODE, and hydrogen(g) will be oxidised to hydrogen ions at the ANODE. Answer (D).

The density of water is 1 g/cm cubed and in order for the pebble to sink its density has to be greater than the density of water and in order for the twig to float its density has to be less than the density of water