I reckon Q3 is D because if you have a look at the reactivity series, Zn is more reactive than Cu so when you add Zn solid to Copper nitrate, the Zn will displace the Cu:
Zn(s) + Cu(NO3)2 (aq) --> Zn(NO3)2 (aq) + Cu(s)
The presence of Cu ions make a solution blue so if they're removed, the...