Sodium bicarbonate is the chemical name for baking powder. Its chemical formula is NaHCO3. What does the subscript 3 mean? A.
There are three molecules of sodium bicarbonate.
B.
There are three molecules of oxygen in sodium bicarbonate.
C.
There are three atoms of oxygen in sodium bicarbonate.
D.
There are three atoms of sodium bicarbonate.

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.  

air

in a tire you fill a tire with air

then a couple days later you check the air pressure in the tire

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