The common metal in Brass,bronze and german silver is

$(a)\;Cu \\(b)\;Mg \\(c)\; Al \\(d)\;Zn$

The common metal in Brass,bronze and german silver is $Cu$
Brass is an alloy of Cu & Zn.
Bronze is an alloy of Cu and Sn
German-silver is an alloy of Cu, Zn and Ni
Hence a is the correct answer.
edited Feb 26