Question

The normal boiling point of liquid hydrogen is $- {253^ \circ }C$ . What is the corresponding temperature on absolute scale?
A) $22\,K$
B) $20\,K$
C) $274\,K$
D) $-20\,K$

Answer 1

To solve the asked question, you need to know the conversion formula of temperature units Celsius $\left( {^ \circ C} \right)$ and Kelvin $\left( K \right)$ which is quite simple and easy to remember in which we add or subtract a constant value to one unit to convert it into the other.

Complete step by step answer:
As told in the hint section of the solution to the asked question, the basic need to solve this question is to know the conversion formula of temperature units Celsius $\left( {^ \circ C} \right)$ and Kelvin $\left( K \right)$ .
First, let us share the conversion formula of temperature units Celsius and Kelvin:
The conversion from Kelvin to Celsius is done by simply subtracting $273$ from the Celsius value of them temperature and can be mathematically represented as:
$^ \circ C = \left( {K - 273} \right)$
From this, we can see that to convert Celsius into Kelvin, we need to transpose, and then the equation becomes:
$\Rightarrow K = {\,^ \circ }C + 273$
Now, to find the normal boiling point of liquid hydrogen on an absolute scale, we need to convert the temperature from Celsius to Kelvin as the absolute temperature scale is generally referred to the Kelvin temperature scale. It is so because when we talk about the absolute zero temperature, i.e. the temperature at which there is no energy and every motion ceases to exist and gases lose all their energy, it lies at $- {273^ \circ }C$ on the Celsius temperature scale, but scientists wanted a temperature unit for which it lies at $0$ on the scale, and hence, invented the new unit Kelvin who's $0$ at the scale coincides with the absolute zero temperature.
To get the answer, we need to substitute the value in the conversion formula of Celsius to Kelvin:
$\Rightarrow K = - 253 + 273$
$\Rightarrow K = 20\,K$

Hence, the normal boiling temperature of liquid hydrogen gas on absolute scale is at $20\,K$ , hence, option (B) is the correct answer.

Note: Many students don’t quite understand what the question means by absolute scale and sometimes may use the conversion formula of Celsius to Fahrenheit which leads them to the wrong answer. Other than that, they may use the conversion formula of Celsius to Kelvin wrongly and instead of adding, may subtract to reach a completely wrong answer.