Which of the following types of intercellular junctions helps in the passage of small molecules and ions?

$P-V$ plots for two gases during an adiabatic process are shown in the figure. Plots $1$ and $2$ should correspond respectively to

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

$A$ body is executing simple harmonic motion. At a displacement $x$ its potential energy is $E_1$ and at a displacement $y$ its potential energy is $E_2$. The potential energy $(E)$ at displacement $(x+y)$ is

Which gases are released when aluminum reacts with concentrated $HCl$ and concentrated $NaOH$ respectively?

What is formed when $HCOOH$ reacts with concentrated $H_2SO_4$?