Abattery produces , which is current that flows in only one direction.

The given blank can be filled with direct.

Explanation:

A battery refers to a chemical apparatus that is used to store electrical energy. A battery generates a direct current that is a current, which flows in only one direction. DC means direct current and it should exhibit fixed terminals, that is, negative and positive terminals, which cannot be altered.  

As the batteries have fixed content, they possess fixed terminals, thus, they can store only direct current. Thus, the batteries produce direct current and produce a voltage in only one direction, and they exhibit a polarity of negative and positive.  

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !