The heaviest naturally occurring element is
a. uranium
c. xenon
b. iron
d. silver

The best answer is a - uranium.

The heaviest naturally occurring element is Uranium. It has a density of 18.95g/cubic cm. Its most common isotope is uranium 238, which has nucleus  that has 92 protons and 146 neutrons.

On earth, it is 40 times more abundant than silver and almost as common as tin. Its half life is 4.47 billion years.

Uranium was discovered by a person known as Martin Klaproth of Germany in the year 1789. He named it after the planet Uranus.

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.