The weather report reads: “Temperature \[{{20}^{\circ }}C\] : Relative humidity \[100\%\] ”. What is the dew point?

Hint: The dew point is the temperature in the atmosphere that varies depending on humidity and pressure, and below which water droplets begin to condense and dew can occur. Or this is the temperature that air needs to be cooled in order to achieve a relative humidity of \[100\%\] .

Complete step-by-step answer:
Before going to the problem, first of all we need to understand the concept of dew point temperature and we will also use the formula which we used to solve the problem.
First, we have to explain the dew point temperature, that is the temperature at which air can hold the maximum amount of moisture present in the surrounding or atmosphere is called dew point temperature. If the temperature is decreased or falls down below this value, some amount of water vapors must condense.
Above information is the general information about the dew point.
We can also say that dew point is a temperature at which saturated vapor pressure is equal to present vapor pressure.
Now, we come to the problem, that is in the question it is given that Temperature \[\text{2}{{\text{0}}^{\circ }}C\] and Humidity is \[100\%\] .
Formula which we used in this problem that is
 \[{{T}_{d}}=T-\dfrac{100-RH}{5}\]
Where \[{{T}_{d}}=\] dew point temperature (in degree Celsius ( \[^{\circ }C\] ))
 \[T=\] Observed temperature (in degree Celsius ( \[^{\circ }C\] ))
 \[RH=\] Relative humidity (in percent ( \[\%\] ))
According to the Given problem we have to find the dew point temperature for data given in the problem.
 \[T=\] Observed temperature (in degree Celsius ( \[^{\circ }C\] )) \[={{20}^{\circ }}C\]
 \[RH=\] Relative humidity (in percent ( \[\%\] )) \[=100\\%\]
We have to substitute these values on formula we get:
 \[{{T}_{d}}={{20}^{\circ }}C-\dfrac{100-100}{5}\]
After simplifying this we get:
 \[{{T}_{d}}={{20}^{\circ }}C\]
As a result, at \[{{20}^{\circ }}C\] the air is saturated.
Hence, \[{{20}^{\circ }}C\] is the dew point.
So, the correct answer is “Option B”.

Note: The dew point temperature, in scientific words, is the temperature at which water vapors in a sample of air at constant atmospheric pressure condense into liquid water at the same rate as it evaporates. We can also say that dew point is a temperature in which saturated vapor pressure is equal to present vapor pressure.