How did dmitri mendeleev organize the periodic table

According with atomic weight and valences

Explanation:

Mendeleev organized the periodic table according atomic weight because the elements exhibit an apparent periodicity of properties, and the magnitude of the weight determines the character of the element

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current

i'm assuming that the correct answer is indeed the first one/ "a"..