Answer:- D. 
Explanations:- In chemical equations, (aq) stands for aqueous, (l) stands for liquid, (g) stands for gas and (s) stands for solid. In double replacement reactions, (aq) means soluble and (s) means insoluble that is precipitate.
Looking at all the equations, it is only the last equation that has a solid product and so this is the only precipitation reaction. A precipitate for Iron(II)carbonate is formed in it.
C. carbon is the correct answer
1.94 * 6. 01 = 11.7 which is approximately same as 11 700. So the answer is 3).
Some acids are capable of drawing water out of an object. This process is called dehydration.
Hope this helped!