Which of the following is not a Lewis acid?

The sound waves of wavelengths $5 ~m$ and $6 ~m$ produce $30$ beats in $3 ~s$. The velocity of sound is: (in $~m/s$)

Assertion $(A)$: The $pH$ of a buffer solution containing equal moles of acetic acid and sodium acetate is $4.8$ ($pK_a$ of acetic acid is $4.8$).
Reason $(R)$: The ionic product of water at $25^{\circ} C$ is $10^{-14} \ mol^2 \cdot L^{-2}$. The correct answer is

The Thomson coefficient of a conductor is $10 \mu V/K$. The two ends of the conductor are maintained at $50^{\circ}C$ and $60^{\circ}C$,respectively. The amount of heat absorbed by the conductor when a charge of $10 C$ flows through it is:

How are the following compounds related?

The potential difference between two parallel plates is $10^4 ~V$. If the plates are separated by $0.5 ~cm$,the force on an electron between the plates is