1.7 km^2 already has two significant figures.
Adding hot cocoa to hot water would be a chemical change
1) Atomic number of magnesium (Mg) is 12, it means that it has 12 protons and 12 electrons.
Electron configuration of magnesium atom: ₁₂Mg 1s² 2s² 2p⁶ 3s².
2) Atomic number of aluminium (Al) is 13, it means that it has 13 protons and 13 electrons., but if it lost one electron, it will have 12 electrons and 13 protons and become aluminium cation Al⁺.
Electron configuration of aluminium cation: ₁₃Al⁺ 1s² 2s² 2p⁶ 3s².
3) Atomic number of silicon (Si) is 14, it means that it has 14 protons and 14 electrons., but if it lost two electrons, it will have 12 electrons and 14 protons and become silicon cation Si²⁺.
Electron configuration of silicon cation: ₁₄Si²⁺ 1s² 2s² 2p⁶ 3s².
Carbon can go either way they can have a 4+ charge (by losing 4 electrons) or a 4- charge (by gaining 4 electrons) to fulfill the octet rule.
I believe the answer is carbon dioxide. Because when carbon dioxide and water combine in the atmosphere it forms a very weak acid called carbonic acid, which falls to the Earth's surface as precipitation.
