Which of the nitrogen oxides is obtained when ammonium nitrate is heated?

Which of the following formulas represents laughing gas?

Ionic radius (in $\mathring{A}$) of $As^{3+}$,$Sb^{3+}$ and $Bi^{3+}$ follow the order:

What is the highest oxidation state possessed by phosphorus in its oxyacids?

The compound$(s)$ which generate$(s)$ $N_2$ gas upon thermal decomposition below $300^{\circ} C$ is (are)
$(A)$ $NH_4 NO_3$
$(B)$ $(NH_4)_2 Cr_2 O_7$
$(C)$ $Ba(N_3)_2$
$(D)$ $Mg_3 N_2$

Phosphonic acid $(H_3PO_3)$ is: