The formal charges of atoms $\left(1\right),\left(2\right)$ and $\left(3\right)$ in the ion ${\left[\begin{array}{l}\underset{\left(1\right)}{\mathrm{O}}=\underset{\left(2\right)}{\mathrm{N}}=\underset{\left(3\right)}{\mathrm{O}}\end{array}\right]}^{+}$ is

Give a reason for the following:

Ionic compounds have a high melting point.

In the given electron dot structure, the formal charge on each nitrogen atom (respectively) from left to right is _______

Two elements $\mathrm{A}$ and $\mathrm{B}$ have electronegativities $1.2$ and $3.0$ respectively. The nature of bond between $\mathrm{A}$ and $\mathrm{B}$ would be