How many significant figures does the following number have: 0.99800

5.

Explanation:

All 5 numbers after the decimal point, including the zeros, are significant.

when [oh-] is 10-5  m, and [h3o+] is 10-9  m, the poh is 5 and ph is 9. again in both cases the sum of ph and poh is 14. however, the hydrogen ion concentration is not always going to be equal to exactly 1 x 10 raised to a negative number. for example, we skipped over the value of 2.0 x 10-7.

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).