What is the frequency of $DC$ (in $Hz$)?

What is the electric charge passing through a cross-sectional area of the conductor per unit time called?

An electric appliance draws a current of $0.4\, A$ when the voltage is $200\, V$. Calculate the amount of charge flowing through it in one hour.

$1\, mA = \dots A$

An electron in a metal is free to move anywhere but cannot leave the metal.

What is the total electric charge on $100$ protons in Coulombs?