Metamerism is a characteristic feature of which of the following?

What is the chemical name of Vitamin $B_1$?

In which group of organisms do the cell walls form two thin overlapping shells that fit together?

The number of roots of the equation $(81)^{\sin ^2 x} + (81)^{\cos ^2 x} = 30$ in the interval $[0, \pi]$ is equal to

The first formed primary phloem is referred to as $A$. The later formed primary phloem is referred to as $B$.
Choose the correct combination of $A$ and $B$.

The density of gold is $19 \ g/cm^3$. If $1.9 \times 10^{-4} \ g$ of gold is dispersed in one litre of water to give a sol having spherical gold particles of radius $10 \ nm$,then the number of gold particles per $mm^3$ of the sol will be