Which equation is a reduction half-reaction that is written correctly?
zn2+(aq) + e– mc004-1.jpg zn(s)
be2+(aq) + 2e– mc004-2.jpg be(s)
2cl–(aq) mc004-3.jpg cl2(g) + 2e–
au(s) mc004-4.jpg au3+(aq) + 3e–

Reduction reaction means addition of electrons. Hence options C and D are rejected.

Coming to the first reduction-half reaction, 
Zn+2 gains 1 electron and forms Zn. It should be Zn+, hence 1st reduction half reaction is also rejected.

So the correct reduction-half reaction is:

Be+2(aq)  +  2e >  Be(s)

Hope this helps!