Q1: What is wrong with this circuit?

ANS:A - The zener is open.

Parallel= voltage is same current different.
Series =voltage is different, current same.

But here r1 and r2 are parallel voltages are different .
So open the diode,r1 and r2 are series so different voltages

i=v/r; r=r1+r2;
i=24/12.5
i=1.92mA
v1=1.92mA*10k ohm=19.2v
v2=1.92mA*2.5K ohm=4.608v (4.7v)

v=v1+v2 = 19.2v+4.608v

=23.8v (24v)