Which of these is an indication that a chemical reaction has occurred? (boiling of a substance ,freezing of a substance, formation of a gas, melting of a substance)

If e is the symbol for an element, which two of the following symbols represent isotopes of the same element? 1. e2. e3. ea.1 and 2c.1 and 4b.3 and 4d.2 and 3

Plz ill give u brainliest which of the following steps is not likely to take place during cellular respiration? a.oxygen combines with carbon of simple sugar. b. energy molecule transfers energy to cells. d. energy is used up.

Magnesium is the limiting reactant in this experiment. calculate the theoretical yield of mgo for each trial. trial 1: trial 2: data mass of empty crucible with lid trial 1: 26.688 trial 2: 26.681 mass of mg metal, crucible, and lid trial 1: 26.994 trial: 2 26.985 mass of mgo, crucible, and lid trial 1: 27.188 trial 2: 27.180