What is 2,100 in scientific notation

2.1 × 10³

Explanation:

In scientific notation we move the decimal place until there is just one number to the left of it in the ones position meaning we would put the decimal in between the 2 and the 1.  To make up for the decimal change we represent it with 10 to a specific power, the power it goes to is how many places we need to move the decimal.  Because in this case we moved it past 3 numbers we will multiply 2.1 by 10 to the 3rd power which will look like this

2.1 × 10³

I hope this helps and please don't hesitate to ask if there is anything still unclear!

the correct answer would be b. amelia, because the particals of gas move really fast (charged particals) and gas also has a lot of room (particals move independently) so the only answer that has both of those is amelia's.