Dehydration occurs between which of the following during its formation?

What is lactose composed of?

Which of the following is a biologically important monosaccharide?

Aqueous solution of carbohydrate with $2$ drops of alcoholic solution of $\alpha$-naphthol and $H_{2}SO_{4}$ gives a ring at the junction. The colour of the ring is:

Sucrose is composed of $......$.

Identify the biological importance of carbohydrates from the following statements:
$1$. In the structure of cell wall.
$2$. As a food storage substance.
$3$. In protein synthesis.
$4$. As enzymes.
$5$. In the structure of $DNA$.