Which of the following order is correct?

Alkaline earth metal carbonates grow more thermally stable as we proceed down the group because they need more warmth to breakdown.

So, the thermal stability order is given as,

${\mathrm{Ca}}_3{\mathrm{N}}_2<{\mathrm{Mg}}_3{\mathrm{N}}_2<{\mathrm{Be}}_3{\mathrm{N}}_2$ (Thermal stability order)

Hence correct option is C.