10 hectometers
One hectometer is 100 meters in length already, so 10 is 1000
Answer 0.5
when reporting calculations from sig figs, report the number of sig figs in the least accurate measurement
so
((2.0265-2.02)/2.0265) x 100.00
((2.0265/2.0265) - (2.02/2.03)) X 100.00
(1.0000 -0.995) X 100.00
0.005 X 100.00
0.5
Two [hydrogen] atoms and one [oxygen] atom