Which is greater, the mass of the compounds before a chemical reaction or the mass of the compounds after a chemical reaction?

the mass of the compounds before is greater.
the mass of the compounds after is greater.
the masses before and after are equal.
it depends on the type of chemical reaction.

Notice how they put future which of the clouds shown would indicate a possible future rain storm? a) b) c) d)

Awelder using a tank of volume 7.50×10^-2 m^3 fills it with oxygen (with a molar mass of 32.0 g/mol ) at a gauge pressure of 3.30×10^5 pa and temperature of 37.1 ∘c. the tank has a small leak, and in time some of the oxygen leaks out. on a day when the temperature is 23.1 ∘c, the gauge pressure of the oxygen in the tank is 2.00×10^5 pa . a) find the initial mass of oxygen. b) find the mass of oxygen that has leaked out.

If a rock weighing 54 n is submerged in a liquid with a density exactly twice that of water, what will be its new apparent weight reading in the liquid?