Final answer:
The number not written in scientific notation is 5 x 10', because it has an apostrophe instead of an exponent, making it not conform to the proper format of scientific notation which requires a coefficient and a power of 10.
Step-by-step explanation:
The number not written in scientific notation is 5 x 10'. For a number to be in scientific notation, it must be written as a product of two factors: a coefficient that is greater than or equal to 1 and less than 10, and a power of 10 written in exponent form. In the given options, while options a), b), and d) all have a coefficient that meets these conditions and a proper exponent, option c) has an apostrophe instead of an exponent, which is not a proper scientific notation format.
To make sure all given numbers are correctly written in scientific notation, they should be expressed in the form of a single digit (or number) followed by a decimal, and then the rest of the significant digits, multiplied by 10 raised to an exponent.