What makes the periodic table such a useful tool? * A. The table lists all the elements in alphabetical order.
B. The table lists all the elements in order of their abundance on Earth.
C. The table groups the elements to show their usefulness.
D. It allows you to compare the properties of the elements.

I think it is D. It allows you to compare the properties of the elements. I might be wrong.

"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"