Which one of the following is a semiconductor?

The correct order of acidic character of the following is:

Identify the incorrect statement about the oxidation states of group $14$ elements.

Explain the following reactions:
$(a)$ Silicon is heated with methyl chloride at high temperature in the presence of copper;
$(b)$ Silicon dioxide is treated with hydrogen fluoride;
$(c)$ $CO$ is heated with $ZnO$;
$(d)$ Hydrated alumina is treated with aqueous $NaOH$ solution.

Of the following acids, the one which has the capability to form complex compounds and also possesses both oxidizing and reducing properties is:

Which of the following does $NOT$ give oxygen upon heating?