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

Parts of a Computer:
(i) Input Unit
(ii) Central Processing Unit (CPU)
(iii) Output Unit

Trachea commonly called wind pipe - allowing the passage of air to lungs.

The entry of food into the wind pipe is prevented by a flap like structure called epiglottis.

The skeletal system consists of bones, cartilages and joints. It provides a framework for the body.

Plant cell,Animal cell and most of fungi.

Cell wall and chloroplast found only in plant cell

We have eukaryotic cells.

If the clothes of a person catch fire,
(i) STOP him where he is
(ii) DROP to the floor if he stands up
(iii) ROLL him on the floor.
Through this activities, we can save the person without big loss.

The roots of a plant take up air from the spaces between the soil particles.

If we remove the fish from the aquarium and keep it in a dark place with green plants,
(i) they can't have sunlight and
(ii) have no CO₂ from the water produced by fish as they breathe.
(iii) Simply say, there is no possibility for photosynthesis to make their food.

When solute is dissolved in a solvent it forms a solution.
Solute + Solvent ⟶ Solution

Yes, we can make a candle doll from candle wax. It is a kind of physical change.

Plants decaying is a chemical change.

K₁, K₂  should be closed.

The expansion of a substance on heating is called, the thermal expansion of that substance.

(i) The measurement of warmness or coldness of a substance is known as its Temperature.
(ii) SI unit of temperature is kelvin

(i) The Water heater
(ii) Iron box
(iii) Electric kettle etc.

While swallowing food if the food particles enter into respiratory tract leads to hiccup and cough to eject out the food particles from respiratory tract.

(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.

The heat is escaping from the room because the room temperature is higherthan atmosphere. Heat energy flows from higher temperature to lower temperature.

(i) Bone provide a frame work for the body.
(ii) Bones along with muscles help in movements such as walking, running chewing and dancing, etc., 

(i) Robert Hook designed the compound microscope.
(ii) He published a book named "Micrographia" in the year 1665.
(iii) He introduce the term cell, which from the latin word "cellula" means a small chamber.
(iv) He observed many objects like Butterfly's wings, Bee's compound eyes under microscope.

During monsoon, the biscuits placed in open lose its crispness. Sugar in biscuits takes up water from the atmosphere and become so soft.

(i) Burning of paper takes place within a short period of time. So, it is a fast change
(ii) In this process, carbon-di-oxide and water are produced with heat and light energies.

A huge envelope of air surrounded the earth is called Atmosphere.
(i) This envelope is thicker near the earth's surface.
(ii) As we go higher up, the density and the availabillty of air gradually decreases.
(iii) Movement of wind, Presence of water vapours for cloud formation are the vital roles of atmosphere.
(iv) Troposphere is the responsible layer for the weather we experience on earth.
(v) Stratosphere has the Ozone layer which protects all life on earth from the harmful UV rays of the sun.

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