According to the mathematical relation between Celsius and Fahrenheit temperature scales,

we have

As we know that the general equation of any straight line is given by where m denotes the slope of the straight line and denotes the intercept of the straight line on the y-axis
Since, in the given figure it is clear that x-axis corresponds to the Fahrenheit temperature scale and the y-axis corresponds to the Celsius temperature scale
By rearranging the equation (1), we get

By comparing equation (2) with equation (3), we can say that the relation between the Celsius and Fahrenheit temperature is a straight line having a slope of and y-intercept as . This means that the straight line representing the relation between the Celsius and Fahrenheit temperature has a positive slope and negative intercept.
Therefore, the required curve representing the relation between the Celsius and Fahrenheit is curve 1 which is lying in the fourth quadrant.