Which of the following are elements? (Select all that apply.)
KCl
Na
C
H2O

Na(Sodium) and C(Carbon) only

Na, C

Explanation:

1. KCl, or potassium chloride, is a combination of two elements- so it's a chemical compound.

2. Na, or sodium, can be found on the periodic table of elements. Therefore, it is an element.

3. C, or carbon, can also be found on the periodic table of elements. Therefore, it is an element.

4. H20, or water, is a combination of 2 hydrogen atoms that bonded into an oxygen atom. Combination of 2 or more elements is a chemical compound.

Therefore, the answers are Na and C.

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.

they are made of gases.

they have a spherical shape.

they make energy through fusion.