Cindy predicts that plastic foam insulates cold drinks better than metal or ceramic materials do. to test the hypothesis, she fills cups made from these materials with equal amounts of cold water. she records the temperature of the water in each cup, using scientific thermometers, every 10 minutes until the water reaches room temperature. which of these conditions must be the same for this experiment to be valid?
a. the thermometer that is in each cup
b. the starting temperature of the water in each cup
c. the ending temperature of the water in each cup
d. the material that makes up each cup

B. The starting temperature of the water in each cup  

Explanation:

Cindy is trying to see if foam or ceramic is a better insulator. Those are her independent variables.

The other variables , like the starting temperature of the water in each cup, must be controlled variables. If she uses different starting temperatures in each cup, she won't know if it was the temperature or the materials that caused her results.

A. is wrong. The thermometers should be identical but, if they aren't, it will make little difference in the results.

C. is wrong. The ending temperature is room temperature, so it is automatically the same for each cup.

D. is wrong. She is trying to measure the effect of different materials.

out of these options:

ability to burn paper

pure sodium reacting violently with water

the boiling point of water

helium does not tend to react with anything

i would say this is a physical property:

helium does not tend to react with anything

why? :

i said helium does not tend to react with anything because well, it reacts to ! but ability to burn paper, pure sodium reacting violently with water, & the boiling point of water are chemical or

physical properties: the properties of a substance that can be observed without changing the chemical makeup of the substance

chemical properties: properties of a substance relating to the chemical nature and reactivity of the substance