Diurnal range of temperature is obtained by

Diurnal range of temperature is the difference between the highest and the lowest temperature of a given day. Therefore, to obtain the diurnal range of temperature, we need to subtract the minimum temperature of the day from the maximum temperature of the same day. Option (c) subtracting the minimum temperature of the day from the maximum temperature of the same day, is the correct method to obtain the diurnal range of temperature. This is because it gives us the difference between the maximum and minimum temperature for a given day, which represents the variation in temperature that occurs within a 24-hour period. Options (a) and (b) are incorrect because they involve adding all the temperature readings, which does not give us the range of temperature for a specific day. Option (d) is incorrect because it gives us the range of temperature for a whole month, rather than a specific day. In conclusion, the diurnal range of temperature is obtained by subtracting the minimum temperature of a day from its maximum temperature.