Thallium shows different oxidation states because

Explain the nature of oxide compounds of group-$15$ elements.

When ammonium dichromate is heated,the gas formed is

Heating white phosphorus with conc. $NaOH$ solution gives mainly

$PCl_3$ reacts with water to form:

An inorganic salt $(A)$ is decomposed at about $523 \ K$ to give products $(B)$ and $(C).$ Compound $(C)$ is a liquid at room temperature and is neutral to litmus paper,while oxide $(B)$ on burning with white phosphorus,gives a dehydrating agent $(D).$ Compounds $(A)$,$(B)$,$(C)$ and $(D)$ will be identified as: