Name the following:
$(a)$ $A$ metal that can be cut with a knife.
$(b)$ $A$ metal that is liquid at room temperature.
$(c)$ $A$ metal that has $3$ valence electrons.

(N/A) Sodium $(Na)$ or Potassium $(K)$ are soft metals that can be easily cut with a knife.
$(b)$ Mercury $(Hg)$ is the only metal that exists in a liquid state at room temperature.
$(c)$ Aluminum $(Al)$ has an atomic number of $13$. Its electronic configuration is $(2, 8, 3)$,meaning it has $3$ valence electrons. Boron $(B)$ also has $3$ valence electrons with configuration $(2, 3)$.