The prefix of ${10^{18}}$ is:
A. giga
B. exa
C. kilo
D. nano
E. mega

Hint: The SI is founded on seven SI basic units for seven basic quantities assumed to be mutually independent. A set of multiple and submultiple prefixes have been adopted for use with the SI units. They may be used with any of the base units and with any of the derived units with special names.

Complete step by step answer:
A measurement is a quantitative observation consisting of two parts-number and scale or unit. These measurements should be accurate. The first step in ensuring accuracy is defining the units in which the measurements are made. Measurement involves comparing the value to be measured with known value.
Scientific notation also referred to as standard form or standard index form is the way of expressing numbers that can easily handle very large numbers or very small numbers. A quantity written in scientific notation as ${\text{M}} \times {10^{\text{n}}}$, where ${\text{M}}$ is the number in decimal number, $10$ is the base and ${\text{n}}$ is the exponent or power of $10$.
A. Giga is equal to ${10^9}$
B. Exa is equal to ${10^{18}}$
C. Kilo is equal to ${10^3}$
D. Nano is equal to ${10^{ - 9}}$
E. Mega is equal to ${10^6}$

Hence, Option B is the correct option.

Additional information:
Each measurement standard has a unit and dimension related to it. Unit is the label given to it and the dimension is what the standard measures. Standards are object or prescription to which all other measurements are compared.


Note:
SI unit prefixes table is given below: