Write the number with appropriate signs: ${{15}^{\circ }}C$ below ${{0}^{\circ }}C$ temperature.

Hint: In this question we have been given with a word problem for which we have to find the solution. We will use the fundamental property of negative numbers to solve this question. We know that in the timeline numbers on the left-hand side are negative numbers and numbers on the right-hand side are positive numbers. Using this property, we will find what is ${{15}^{\circ }}C$ below ${{0}^{\circ }}C$ temperature.

Complete step-by-step solution:
We have to write the number with the appropriate sign representing ${{15}^{\circ }}C$ below ${{0}^{\circ }}C$ temperature.
We know that the temperature scale of degrees has positive as well as negative temperatures and ${{0}^{\circ }}C$ is in the middle of the scale.
Now ${{15}^{\circ }}C$ below ${{0}^{\circ }}C$ temperature shows that the temperature is negative therefore, the way to find the temperature is to subtract ${{15}^{\circ }}C$ from ${{0}^{\circ }}C$.
On subtracting, we get:
$\Rightarrow {{0}^{\circ }}C-{{15}^{\circ }}C$
On simplifying, we get:
$\Rightarrow -{{15}^{\circ }}C$, which is the required solution.
Therefore, the number with the appropriate sign when ${{15}^{\circ }}C$ below ${{0}^{\circ }}C$ temperature is $-{{15}^{\circ }}C$.

Note:It is to be remembered that in the degree temperature scale, lower temperature resembles coldness and higher temperature represents hotness. There also exist other scales of measuring temperature which are Fahrenheit and Kelvin. The scale of Kelvin is different that of degrees or Fahrenheit because there are no negative temperatures on its scale since its zero starts at absolute zero. It is to be remembered that when a negative number is subtracted from a positive number, the greater numbers sign will be of the result.