Elements $X$, $Y$ and $Z$ all lie in the first two periods of the Periodic Table. Their Pauling electronegativity values, $E_N$, are given as follows: $X = 1.0$, $Y = 2.1$, $Z = 4.0$. Substances with formulae $XZ$, $YZ$ and $Z_2$ are known to exist. Which row arranges these substances in increasing order of melting point?
- Alowest: $XZ$ $\rightarrow$ $YZ$ $\rightarrow$ $Z_2$ highest
- Blowest: $XZ$ $\rightarrow$ $Z_2$ $\rightarrow$ $YZ$ highest
- Clowest: $Z_2$ $\rightarrow$ $YZ$ $\rightarrow$ $XZ$ highest
- Dlowest: $Z_2$ $\rightarrow$ $XZ$ $\rightarrow$ $YZ$ highest