Pili or fimbriae are associated with which process?

Amongst $TiF_6^{2-}$,$CoF_6^{3-}$,$Cu_2Cl_2$ and $NiCl_4^{2-}$,the colourless species are:

Assertion $(A)$: $A$ catalyst increases the rate of a reaction.
Reason $(R)$: In the presence of a catalyst,the activation energy of the reaction increases.
The correct answer is

If $C$ is the midpoint of $AB$ and $P$ is any point outside $AB$,then:

The general solution of the differential equation $\frac{y dx - x dy}{y} = 0$ is

Photoelectric emission is observed from a metallic surface for frequencies $v_1$ and $v_2$ of the incident light rays $(v_1 > v_2)$. If the maximum values of kinetic energy of the photoelectrons emitted in the two cases are in the ratio of $1 : k$,then the threshold frequency of the metallic surface is