Explanation:
a. K Na Li
melting point decreases a
down the group since more shells are added down the group hence the the attractive force that the protons exert on the electrons decreases down the group and hence melting point also decreases down the group.
i.e Li,Na,K decreasing order.
And hence the increasing order will be:
K Na Li.
b. Na Mg Al
Effective nuclear charge increases across the period and hence melting point increases across the period since Al Mg and Na are in the same period hence the increasing order will be Na Mg Al.
