Which factor is least likely to cause a memory problem

Can someone me with 3 and 4 plz. this is for masteries test.

Which statement best describes the function of enzymes?

Isopropyl alcohol, (ch3)2choh, is a common solvent. determine the percent by mass of hydrogen in isopropyl alcohol. a) 6.71% h b) 13.4% h c) 25.0% h d) 53.3% h