We need to compare some numbers to the measured temperatures and find out which is the one that is less than -1.9 and 2.4.
In order to do so, we can put those values on a number line. Remember that the numbers located to the right of zero are positive and the ones located to the left of zero are negative (the farther they are from zero, the more negative they are):
Notice that the numbers on the left are smaller than the ones on the right of them.
Therefore, as we see above, the only given number that is less than -1.9 is the number -2.6 (which is also less than 2.4).
Thus, the answer is -2.6º Celsius.