1-There are 18 volcanoes in the US with the potential to erupt again, all of them in Alaska, Hawaii and the West Coast states.
2-Rubies and sapphires are actually the same mineral - corundum. The basic chemical formula of corundum is Al2O3, but traces of iron stain the mineral red (ruby) while traces of chromium or titanium stain the mineral blue (sapphire).
3-Rubies, sapphires and emeralds are all more rare than diamonds.
4-Not all diamonds are transparent. They come in a variety of colors (called "fancies"), including yellow, green, blue, orange, brown ("champagne"), purple, grey, black (called carbanado, recently shown to be meteroic), milky white, pink, and red. Red is by far the rarest.
5-Antacids taste like chalk because they ARE chalk, a.k.a. calcium carbonate.
If two gases with pressures of 2 atm and 3 atm are mixed at constant temperature, the total pressure will be the sum of the two pressures. Therefore the answer is D. 2 atm + 3 atm or 5 atm will be the total pressure of the gas mixture.
