Final answer:
The greater number between 3.4 x 10^8 and 7.2 x 10^19 is 7.2 x 10^19 because it has a larger exponent, indicating a much larger value.
Step-by-step explanation:
The question requires us to identify the greater number between 3.4 x 10^8 and 7.2 x 10^19. To determine which is greater, we compare the exponents of 10, since the base number 10 is the same for both numbers. The number with the higher exponent has a greater value because the base number is being multiplied by itself more times.
In our case, the number 7.2 x 10^19 has a larger exponent (19) compared to the exponent (8) of 3.4 x 10^8. Hence, 7.2 x 10^19 is the greater number. We don't even need to compare the coefficients (7.2 and 3.4) because the exponent difference is far greater and determines the size in this context.