If the theoretical yield of a reaction is 0.156 g and the actual yield is 0.151 g , what is the percent yield?

Simply put, you can calculate a reaction's percent yield by dividing the actual yield, which is what the reaction actually produces, by the theoretical yield, which is what the reaction should theoretically produce, and multiplying the result by 100 .

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.

it would be a gas formation