Which of the following does not exist?

In the carbon family,elements other than carbon do not form $p\pi - p\pi$ bonds because their atomic radii are very ........

When a colored gas is passed through bromine water,the color is discharged. Which gas is it?

Which gas burns with a blue flame?

Reaction of an inorganic sulphite $X$ with dilute $H_{2}SO_{4}$ generates compound $Y$. Reaction of $Y$ with $NaOH$ gives $X$. Further,the reaction of $X$ with $Y$ and water affords compound $Z$. $Y$ and $Z$,respectively,are:

Which of the following products is formed when $SiF_4$ reacts with water?