Volume

17 It is known that droplets of a certain chemical have a volume of 0.02 cm3 (rounded to the nearest 0.01 cm3).
What is the maximum number of droplets of the chemical that can be mixed with 10 cm3 of water (rounded to the nearest 10 cm3) if the resulting solution must not have more than 1 % of the
chemical in?

A 2
B 4
C 5
D 6
E 10

What percentage of the resulting solution is water? You know that that percentage is 10 cm3.

99%

So if 99% is 10 cm3, what is 1%?

10/99

so that is the maximum volume of your droplets of chemical.

17 It is known that droplets of a certain chemical have a volume of 0.02 cm3 (rounded to the nearest 0.01 cm3).
What is the maximum number of droplets of the chemical that can be mixed with 10 cm3 of water (rounded to the nearest 10 cm3)

I think you may be missing the significance of the rounding comments, although I do wonder if the bit I've emphasized below is accurate:

The first rounding comment doesn't change what I said, it just means that, if the droplets are at the small end of the range, more droplets can make up the volume of chemical.

The second rounding comment made no sense on my first few readings of it, as I could not see how the "number of droplets" could be rounded to the nearest 10 cm3.

On re-reading it for the umpteenth time, I now realise that it is the volume of water that is rounded to the nearest 10 cm3, which is odd, as you say. It appears to mean that the volume of water is somewhere between 5 and 15 cm3. To get the maximum number of droplets, we need to work with the largest volume of water (15 cm3) and small droplets of chemical.

OK so the largest volume is 15cm and the smallest droplet should be 1.5cm. What next?

Do the sums again with 99% is 15 cm3, instead of 10 cm3.
The smallest droplet should be 0.015 cm3.

Whoops my bad.
So 1% is 15/99
So the number of drops must not exceed the value of 15/99cm3 which is around 0.15?