For a complex reaction the reaction progress curve
a)has several hills and valleys
b)has only one peak
c)is a flat line
d)shows energy vs. pressure

a) has several hills and valleys

Explanation: Elementary reactions are reactions which takes place in one single step and thus contains only a single peak.

Complex reactions are reactions which cannot take place in one step but takes place in a sequence of number of steps.

In a complex chemical reaction, the reactant molecules pass through different transition states due to bond breaking and bond making. Here the species stays for a very short period, usually called transition period of activated complex.

"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"