Answer: 4.2 x 10⁻⁴m
Step-by-step explanation: Scientific Notation is a method of writing a very large or very small number. It consists in any real number between 1 and 10 multiplied by any power of 10 (positive or negative).
The diameter of hydrogen is 5x10⁻¹¹m. There are 8.4x10⁸ atoms of hydrogen.
To determine the length of the line of atoms, you could add the diameter the number of atoms or multiply the diameter by the number of atoms:
L = 5x10⁻¹¹ * 8.4x10⁸
As it is multiplication, you can mutiply the numbers and then add the power of 10, since they are in the same base:
L = 42 x 10⁻³m
or moving comma to the left:
L = 4.2 x 10⁻⁴m
The length of the line of hydrogen atoms, in scientific notation is 4.2x10⁻⁴m