How many independent variables are allowed in an experiment

Aspirin has a density of 1.40 g/cm3 what is the volume in cubic centimeters of a tablet weighing 320 mg ?

This question is about electrolysis. metal spoons can be coated with silver. this is called electroplating. suggest one reason why spoons are electroplated?

Consider hydrogen in an excited state n = 5n=5 that emits photons to reach the ground state. there are various possible transitions other than straight to the ground state that can occur; for example, it can drop to the n = 3n=3 state followed by the n = 3n=3 to the ground state transition. which of the possible transitions will result in the emission of a photon in the visible region?