A(a) is a pure substance that cant be broken down into simpler substances by chemical or physical means
a) element
b) mineral
c) chemical
d) atom

Explanation:

There are two kind of substances that may be classified as pure substances: elements and compounds.

Elements are the pure substances whose atoms are all of the same kind (same atomic number). Some xamples of pure substances are sodium (Na), oxygen gas (O₂), hydroge gas (H₂), nitrogen gas (N₂), helium (He), and gold (Au). There are 118 known elements. You can find all of them in a periodic table.

Elements cannot be broken down into simpler substances by chemical or physical means because the simplest substance is the atom.

The only way to break elements into other substances is by nuclear reactions: fission and fusion reactions transform the atoms of an element into different atoms, but those reactions are not considered either chemical or physical changes. Nuclear reactions are a completely different kind of changes.

On the other hand, the other kind of pure substances, compounds, are formed by two or more different elements, and they can be broken down into simpler substances by chemical means. For example, water molecules (H₂O) can be broken down into the elements that constitue them, i.e. hydrogen and oxygen.

a rain shadow is a dry region of land on the side that is protected against the prevailing winds of a mountain range. the prevailing winds are the winds that occur most of the time in a particular place of the earth

prevailing winds carry air toward the mountain range. as the air rises up over a mountain range, the air cools, water vapor condenses, and clouds form. on this side of the mountains, called the windward side, precipitation falls in the form of  rain  or snow. this dry air produces a  rain shadow.

i think its 5049.

i hope this !