Questions received from a curious UG student

I have several doubts in physics.Would you like to answer me please?The following are the doubtful questions I have -
1.What is meant by 'Radic'?
2.What is a 'parallelopiped'?Is it a 3-dimensional parallelogram?
3.Why does no electric current flow through vacuum?
4.When several transparent materials are kept above each other, the resultant behaves like an opaque object.Why?What's the Optics  behind it?
5.Why the ray of light passing through the centre of curvature of a concave mirror behave as normal while it doesn't behave as normal when it passes through other points on the principal axis?
6.Why the ray of light passing through optical center of a lens passes undeviated while when it passes through other points on the interface of the lens, it gets refracted?
7.What is the force opposing gravity of earth or simply gravitational force?(We can use this to invent magic broomstick like in harry potter movies!!!..)
8.(i)A 3-dimensional space consists of how many planes?(My supposition is Infinite)
   (ii)A hyperspace consists of how many planes?
9.Why is the interface of concave/convex lens inside the the lens while it is on the boundary of a rectangular glass slab?
10.Does the flow of all sub-atomic/universal particles constitute electric current?If not, why? If yes,  then how can there be charges of two types i.e. +ve and -ve?
11.From where does charges arise in electrons and protons?
12.What is the difference between viscosity and elasticity?
13.What are the differences between space and vacuum?