Helium has a density of 1.79 x 10-4 g/ml at standard temperature and pressure. a balloon has a volume of 6.3 liters. calculate the mass of helium that it would take to fill the balloon. be sure to follow significant figure rules when calculating the answer.

If a polyatomic ionic compound has gained two hydrogen ions, then how does its name begin?

Sally is making a model of a magnesium atom with an atomic mass number of 24 for her chemistry class. she has foam balls for the protons, neutrons, and electrons. she has added 6 neutrons to her model so far. how many more neutrons does she need to add to complete her neutral atom of magnesium?

What is the main reason why some developing countries fear the increase the free trade policies around the world?