Among the following,which is water insoluble?

The wavelengths of light used in an optical instrument are ${\lambda _1 = 4000 \ \mathring{A}}$ and ${\lambda _2 = 5000 \ \mathring{A}}$. The ratio of their respective resolving powers (corresponding to ${\lambda _1}$ and ${\lambda _2}$) is:

What is the product obtained in the following reaction?

The Cartesian form of the polar equation $\theta = \tan^{-1} 2$ is

Which one of the following is not an essential mineral element for plants while the remaining three are?

Which one is a wrong statement?