Which is an amphoteric oxide?

When $MnO_2$ and $H_2SO_4$ are added to a salt $(A)$,the greenish yellow gas liberated indicates that salt $(A)$ is:

The basic structural unit of feldspar,zeolites,mica and asbestos is

Heating silicon with which of the following at high temperature produces carborundum?

The gas produced by the passage of air over hot coke is

State True or False for the following statements:
$(1)$ Fullerene has $20$ rings of $6$ members and $12$ rings of $5$ members.
$(2)$ $CO$ is neutral while $CO_2$ is acidic.
$(3)$ Boron fibres are used in making light composite material for aircraft.
$(4)$ When borax is heated in a Bunsen burner flame with $CoO$ on a loop of platinum wire,a yellow coloured $Co(BO_2)_2$ bead is formed.