Answer:
1 x 10^-4
Explanation:
Use the equation pH = -log[OH-}
Rearranging it [OH-] = 10^-pH
Plugging in we get [OH-] = 1 x 10^-4
Silicon, it's bring brother would be the prime candidate, although its compounds are notably different from those of carbon.
Oxygen = 16
Iron = 55.8
16 x 27.6% = 4.4 /4 = 1.1
55.8 x 72.4% = 40.4 /4 = 10.1
1 oxygen and 10 iron, so Fe10 O