Answer: a.
kilograms
Explanation:
Scientific notation: A mathematical expression used to express a very large or a very small number in a product of a decimal number between 1 and power of 10 .
Given : Jacob learns that the mass of a new planet found in the solar system is 2,330,000,000,000,000,000,000,000 kilograms.
Here, in 2,330,000,000,000,000,000,000,000 (A very large number)
Total digits = 25
Power of 10 = Total digits -1= 25-1=24
In scientific notation:

Hence,
kilograms is the mass represented in scientific notation.