Movement of molecules from an area of higher concentration to one of lower concentration is called Diffusion
I'd go for D here. It also fits in with the idea of thermal expansion - as something is heated up, molecules vibrate and maybe collide. they vibrate with bigger amplitudes, so taking up more space, so expanding. maybe
Explanation:
The scientific notation:

where
and k is integer.
We have the example:

You can write the numbers in a "normal" form:

Make the sum:

And next write it in the scientific notation:

<h3>Other method:</h3>
You can add numbers in scientific notation if the power of tens in both number is the same.
Therefore you must convert the first number:

Now, you can make the sum:

The statement that describes a chain reaction brought about by a nuclear reaction is "neutrons <span>released during a fission reaction cause other nuclei to split." This is applicable to fission reactions only wherein atoms split and produce neutrons that also cause further atoms to split, thus creating a chain or series of reactions.</span>