How many atoms are represented?
KBr
C12H22O11
KAlSi3O8
Ag3PO4
CH3CO2C6H4COOH

Explanation:

An atom is the smallest indivisible particle that takes part in any chemical reaction. They are easily identified distinctively as elements in a compound.

The subscripts accompanying a chemical symbol shows the number of atoms of elements combining to give a compound:

 Compound                       Elements                         Number of atoms

     KBr                            K                Br                                 2

C₁₂H₂₂O₁₁                  12(C)      22(H)    11(O)                  12 +  22 + 11 = 45

KAlSi₃O₈                  1(K)     1(Al)    3(Si)   8(O)               1 + 1 + 3 + 8  = 13

Ag₃PO₄                       3(Ag)     1(P)        4(O)                3+ 1 + 4        = 8

CH₃CO₂C₆H₄COOH     9(C)    8(H)    4(C)                     9+8+4  = 21

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"