The answer is 1.75 x 10¹⁰ m.
Scientific notation refers to a mathematical expression that is used to represent a decimal number between 1 and 10 multiplied by ten, or we can say that to write a large numbers using less digits.
Diameter of chlorine atom = 175 picometers (pm)
175 pm = 0.000000000175 m
in scientific notation we will write 0.000000000175 m as 1.75 x 10¹⁰ m