Please solve this please ​

Ibeg i need 20. a reaction produces 4.93 l of oxygen, but was supposed to produce 1 mol of oxygen. what is the percent yield?

How much would you need to weigh out in order to have 0.2moles of magnesium atoms?

Many radioactive atoms that have large masses undergo radioactive decay by releasing a particle that is identical to a helium-4 nucleus. what changes in the original atom are expected as a result of this natural phenomenon? the atomic number and the mass number will decrease. the atomic number and the mass number will increase. the atomic number will increase, and the mass number will decrease. the atomic number will decrease, and the mass number will increase.