Switch, Bulb and Battery are the parts of the electric circuit. Generator is the source of electricity.

Simple circuit is there in a torch light.

The Iron chain is the conductor from the above figures.

yes, I can produce electricity from lemon. Because lemon juice (Acetic acid) acts like a electrolyte.

K₁, K₂  should be closed.

Silver is not used to make electric wires because it is expensive.

No the cell used in the clock cannot give us an electric shock because the voltage is very low in the cell.

Conductors:
(i) The rate of flow of electric charges in a circuit is called electric current.
(ii) The materials which allow electric charges to pass through them are called conductors.
(iii) Examples: Copper, iron, aluminium, impure water, eafth etc.
Insulators (Non -Conductors) : 
(i) The material which do not allow electric charges to pass through them are called insulators or non- conductors.
(ii) Examples: plastic, glass, wood, rubber, chinna clav, ebonite etc.

We get electricity from thermal power, hydel power, tidal power wind power, solar power etc as sources of electricity
Thermal Power stations:
In thermal power stations, the thermal energy generated by burning coal, diesel or gas is used to produce steam. The steam is used to rotate the turbine. While the turbine rotates, the coil of wire kept between the electromagnet rotates. Due to electro magnetic induction electricity is produced. Here heat energy is converted into electrical energy.
Hydel power stations:
In hydel power stations, the turbine is made to rotate by the flow of water from dams to produce electricity. Here kinetic energy is converted into electrical energy. Hydel stations have long economic lives and low operating cost.
Atomic power stations:
In atomic power stations, nuclear energy is used to boil water. Here the steam is used to rotate the turbine. As a result, electricity is produced. Atomic power stations are also called as nuclear power stations. Here nuclear energy is converted into mechanical energy and then electrical energy.
Wind Mills:
In wind mills, wind energy is used to rotate the turbine to produce electricity. Here kinetic energy is converted into electrical energy.

(i) Yes, the bulb will glow.
(ii)  A piece of zinc metal (such as a galvanized nail) and a piece of copper are inserted into a lemon and connected by LED bulb.
(iii) The zinc and copper are electrds and the juice (acetic acid) is a electrolyte.
(iv) Power generated by reaction of the metals in acetic acid.

Both A and R are correct and R is the correct explanation for A.