To find the number of hydrogen atoms necessary to have a length of one nanometre, we need to consider the given radius of a hydrogen atom, which is 10^(-10) meters.

First, we need to convert the length of one nanometre to meters. One nanometre is equal to 10^(-9) meters.

To calculate the number of atoms, we divide the length (in meters) by the radius of each atom (in meters).

The calculation is as follows:

(10^(-9) meters) / (10^(-10) meters) = 10

So, 10 hydrogen atoms will be necessary to have a length of one nanometre.

Therefore, the correct answer is option 2, which states that 10 hydrogen atoms are required.