Why does the density of a substance stay constant even if the mass of the substance increases?

If the mass stays constant the object's density decreases as the volume increases. ... Because the property of density is a constant for all variables, density can be used to identify the material an object is made of.

Explanation:

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.

some sources quote the lethal dose, for an average 170lbs opiate-naive individual is between 75 and 375 mg