Question

Absolute zero on Kelvin scale is equal to
(A) 273 K
(B) 0 K
(C) 373 K
(D) 15 K

Answer 1

Hint
Absolute zero is the lowest temperature that can ever be achieved. The average kinetic energy of a gas becomes zero when the gas is in absolute zero temperature. So the absolute zero will be the lowest value on the Kelvin scale which is possible.

Formula used: In this solution we will be using the following formula,
$\Rightarrow {\bar E_k} = \dfrac{3}{2}kT$ where ${\bar E_k}$ is the average kinetic energy of the molecules of a gas, $k$ is the Boltzmann constant and $T$ is the absolute temperature of the gas.

Complete step by step answer
The temperature of a substance is a measure of the average kinetic energy of its molecules. When the average kinetic energy of the molecules is high, the temperature is said to be high and when the average kinetic energy is low, the temperature is said to be low too.
Specifically, for gasses, the average kinetic energy is directly proportional to the Absolute temperature in Kelvin. i.e.
$\Rightarrow {\bar E_k} \propto T = KT$ where $K$ is the constant of proportionality. The value is $\dfrac{3}{2}k$ where $k$ is the Boltzmann constant. Hence,
$\Rightarrow {\bar E_k} = \dfrac{3}{2}kT$
Making $T$ subject we have
$\Rightarrow T = \dfrac{2}{3}\dfrac{{{{\bar E}_k}}}{k}$
From prior knowledge, we know that the minimum kinetic energy that can ever be possessed by a body is zero, hence minimum temperature corresponding to the minimum kinetic energy is given as
$\Rightarrow T = \dfrac{2}{3}\dfrac{{\left( 0 \right)}}{k} = 0$,
Hence, the minimum temperature on the Kelvin scale is zero. This is the absolute zero. So the correct answer will be option (B).

Additional Information
There are other temperature scales besides the Kelvin scale such as the Celsius scale, and the Fahrenheit scale. These scales have a relationship with one another, and thus temperature in one scale can be converted to another.

Note
In actuality, absolute zero is extremely difficult to be achieved and, to this day, has never in history been achieved even with the best cooling techniques. The cold temperature of space is at 3K.