Which one of the following phosphorus halides contains both tetrahedral and octahedral shaped ions in its solid state?

Which of the following is least stable?

Give reasons: $A$ mixture of dilute $NaOH$ and aluminium pieces is used to open blocked drains.

$A$ certain element forms a solid oxide which when dissolved in water forms an acidic solution. The element is:

What are allotropes? Sketch the structure of two allotropes of carbon namely diamond and graphite. What is the impact of structure on physical properties of two allotropes?

$A$ solid element $Y$ conducts electricity and forms two types of chlorides: $YCl_n$ (a colorless volatile liquid) and $YCl_{n-2}$ (a colorless solid). To which group does element $Y$ belong?