When orthoboric acid $(H_3BO_3)$ is subjected to strong heating, the residue left is

Which one of the following statements is not correct?

The chemical name of borax is

Which of the following compounds is formed as a blue bead when borax is heated with cobalt oxide?

The correct formula of borax is $Na_2[B_4O_5(OH)_4] \cdot 8H_2O$. If the formula is represented as $Na_2[B_4O_5(OH)_x] \cdot yH_2O$, then the sum of $x$ and $y$ is:

The element that combines with oxygen to give an amphoteric oxide is