It is a substance which changes the colour of reflected or transmitted light
For example chlorophyll have green pigments
Remember that a controlled variable is a variable that stays the same thoughout the experiment.
it wouldn't be a. because two different wires were used
the final length of the wax would be your dependent variable, so it wouldn't be c.
the thermal conductivity is the independent variable so it isn't d.
the original length of the wax was the same for both.
So B is your answer.
On site means insitu.
invitro means in glass like a test tube.
