Which of the following chemical reactions is an oxidation-reduction reaction?
a. cuso4 + bacl2 yields baso4 + cucl2
b. pb(no3)2 + 2nacl yields pbcl2 + 2nano3
c. n2 + 3h2 yields 2nh3
d. k2so4 + bacl2 baso4 + 2kcl

"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"

it's all four options.