You solve a problem to find the charges on three objects. Your calculations lead you to conclude that the objects have charges of:
Q1 = 5 x 10-15 C
Q2 = 5 x 10-19 C
Q3 = 5 x 10-23 C
Are any of these results clearly incorrect?
Charge is quantized - it comes in integer multiples of the elementary charge
e = 1.60 x 10-19 C.
Q3 is definitely wrong - the charge is far too small. It represents a small fraction of e, which is impossible. The other two answers are fine, although Q2 is probably 3e, 4.8 x 10-19 C.
Note that quarks have fractional charge (a charge with a magnitude less than e), but the magnitudes are e/3 and 2e/3. In general we won't deal with quarks in this course.