Heating an alkali metal nitrate usually breaks it down into the metal nitrite plus oxygen, not into the metal oxide plus nitrogen dioxide. Sodium nitrate follows exactly this common pattern, $2NaNO_3 \rightarrow 2NaNO_2+O_2$, so no brown $NO_2$ fumes appear.
Lithium is the odd one out among the alkali metals. Because the lithium ion is unusually small and highly polarising, lithium nitrate behaves more like a typical ionic nitrate of a small, highly charged cation and decomposes all the way to the oxide, releasing both $NO_2$ and $O_2$.
Magnesium and calcium, being group 2 metals, also form small, more polarising cations, so their nitrates likewise decompose to the metal oxide with evolution of $NO_2$ and $O_2$.
Sodium is therefore the only metal in the list whose nitrate decomposes without releasing nitrogen dioxide. The correct choice is option (2).
Which of the following statements are true?
A. Unlike Ga that has a very high melting point, Cs has a very low melting point.
B. On Pauling scale, the electronegativity values of N and C are not the same.
C. $Ar, K^{+}, Cl^{–}, Ca^{2+} and S^{2–}$ are all isoelectronic species.
D. The correct order of the first ionization enthalpies of Na, Mg, Al, and Si is Si $>$ Al $>$ Mg $>$ Na.
E. The atomic radius of Cs is greater than that of Li and Rb.
Choose the correct answer from the options given below: