PREDICT THE REACTION MG(NO3)2(AQ)+NA(S)

In the activity series, Na is more reactive than Mg, thus it can displace Mg:

Mg(NO3)2 + Na -> NaNO3 + Mg

Balancing the reaction,

Mg(NO3)2 + 2Na -> 2NaNO3 + Mg

Hope this helps :)