The cell membrane keeps harmful chemicals out of animal cells.
I would say that the answer is d?
Answer: Decreases across the period and increases down the group
Answer:

Explanation:
Mass of one tablet = 20 mg
Mass of two tablets = 
Percent that is soluble in water = 40%
Mass of tablet that is soluble in water = 
So, mass of solute is 
Density of water = 1 kg/L
Volume of water = 1 L
So, mass of 1 L of water is 
PPM is given by

Hence, the concentration of iodine in the treated water
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The two samples will have the same density because they are the same substance. The volume will have increased just enough to balance the greater mass. Key Concept- When substances have the same volumes but different masses, the substance having the greatest mass will be the most dense.