Answer:
it tells you that the speed increases until about 20 seconds then keeps a steady pace for 20 seconds then the speed drops and stops at 55 seconds in the process.
Balanced equation is:
2Mn+4CuCl——->4Cu+2MnCl2
a=2
b=4
c=4
d=2
One charge is enough in order to have an electric field.
In fact, every charge generates an electric field: for example, the electric field generated by a single point positive charge is radial, as shown in the attached figure. More complicate electric field configurations can be obtained adding charges or using more complicate charge distributions, but one charge is enough to have an electric field.