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Generator is a device for producing electric current. So, choice (i) is correct.

(a), (c) are true statements. 

(b) Magnesium is a combustible metal 

(d) Calorific value of coal is higher than that of wood.

(d) kilojoule per kilogram

The amount of heat produced by the complete burning or combustion of 1 Kilo gram of a fuel is called its calorific value. The calorific value of a fuel is expressed in the unit of Kilo joules per kilogram.

The calorific value of fuel is the amount of heat produced by the complete combustion of 1 kg of fuel. 

Now, 

Heat produced by 4.5 kg of fuel = 180000 kJ Therefore, heat produced by 1Kg of fuel = 180000/4.5 = 1KJ/Kg 

= 40,000 kJ/kg 

Hence, the calorific value of the fuel is 40,000 kJ/kg. 

The calorific value of a fuel is expressed in kilojoules per kilogram (kJ/kg).

Hint: 

Types of fuels 

Solid fuel – Coal, wood, etc. 

Liquid fuel – Kerosene oil, petrol etc. 

Gaseous fuel – CNG, LPG etc. 

Uses 

Coal – cooking etc. 

Kerosene oil – Fuel for stoves, lamps etc. 

LPG – Fuel for industry etc.

Hint: 

(i) Wood produces lot of air pollution. 

(ii) Use of wood as fuel encourages cutting of trees leading to deforestation.

Burning of coal, petrol and diesel produces sulphur dioxide which goes into the air. It is an extremely suffocating and corrosive gas. It may damage our lungs. The burning of petrol and diesel in the engines of vehicles also releases nitrogen oxides into the air. These oxides produced by the burning of fuels dissolve in rain water and form acids. The rain water containing acid is called acid rain. It is harmful for crops, soil and damages buildings.

A solenoid is a device which is formed when an insulated current-carrying wire is bent into a coil with an N number of loops or turns. It is like wrapping of a wire on a cylindrical object. The individual magnetic field of each turn contribute and it results into a magnetic field which is like the magnetic field of a bar magnet. 

The magnitude of magnetic field depends on following factors: 

•Number of loop/turns. 

•Amount of current. 

•Material inside the cylinder. 

In these factors amount of current and number of turns play the major role. Both are directly proportional to the magnetic field produced and can be used as a factor to produce strong electromagnetic field.

True.

The formula for the magnetic field of solenoid and most of the electric appliances is directly proportional to current passing through it.

B ∝ I

When we pour water on the fire it cools the temperature of the combustible material so that its temperature is brought below its ignition temperature. This prevents fire from spreading. Water vapours also surround the combustible material, helping in cutting off the supply of air. So, the fore is extinguished.

Difference between ion and atom:

Difference between cation and anion:

It depends upon :

(i) The direction of current through the conductor. 

(ii) The detection of the magnetic field in which the conductor is placed.

About 100°C to 140°C

By increasing the current flowing in the conductor; by increasing the strength of magnetic field. 

(a) Combustible — charcoal, straw, card board, paper, candle wood, 

(b) Non-combustible — chalk, stone, iron rod, copper coin, glass.

C. natural gas 

The use of petrol and diesel as fuels in automobiles is being replaced by CNG because it produces very small amount of harmful gases.

A chemical process in which a substance reacts with the oxygen to give heat and light is called combustion. The light which is given off during combustion can be in the form of flame or as a glow. The substance which undergoes combustion is said to be combustible. It is called fuel.

LPG is a better domestic fuel than wood due to: 

1. LPG has higher calorific value, so it produces much more heat on burning than an equal mass of wood. 

2. It burns without leaving behind any smoke. 

3. It burns completely without leaving behind any solid residue but wood leaves behind a lot of ash on burning.

An example of gaseous fuel is compressed natural gas ( CNG ).

A. bio gas 

Bio gas has calorific value of 40000 Kj/Kg.

B. spirit 

Spirit/petrol has the lowest ignition temperature and can catch fire easily.

B. white phosphorus 

White phosphorus undergoes spontaneous combustion. Hence it is not used in making matchsticks now days.

According to this rule, stretch the thumb, fore finger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of Magnetic field and the second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.

Those substances which do not burn are called non-combustible substances. 

For Ex: Stone, cement, glass, bricks, soil, sand, water, iron nails, copper objects.

The Right option is : (b) glass

Those substances which can burn are called combustible substances. 

For Ex: Cloth, straw, cooking gas, kerosene oil, wood, coal, charcoal etc. A combustible substance is called as fuel

C. asbestos 

Asbestos is a non combustible substance and cannot catch fire on its own.

Food is the fuel for our body because in our body food is broken down by reaction with oxygen and heat is produced.

When coil is moved towards a stationary magnet, the magnetic field associated with the coil will change and so current will be induced in the coil. This causes galvanometer to show deflection in one direction. Now when coil is moved away, the magnetic field will decrease and so current induces in the opposite direction causing galvanometer to show deflection in opposite direction. The phenomenon is electromagnetic induction.

Combustible substance – The substance that undergoes combustion is said to be combustible.

Example - Petrol

Non-combustible substance - The substance that does not undergo combustion is said to be non-combustible.

Example – Iron

The answer is (c) a permanent magnet to rotate the armature

In electric motors Electro magnet is used instead of permanent magnet.

In commercial electric motors: 

i. the coil is wound on a soft iron core. This increases the strength of magnetic field, which makes the motor more powerful. 

ii. the coil contains a large number of turns of insulated copper wire. 

iii. a powerful electromagnet is used in place of permanent magnet. 

(i) When a bar magnet is pushed into the coil, a momentary deflection is observed in the galvanometer. This deflection indicates that a momentary current is produced in the coil.
(ii) When a bar magnet is held stationary inside the coil, there is no deflection in the galvanometer. It indicates that no current is produced in the coil.
(iii) When a bar magnet is withdrawn from the coil, the deflection of the galvanometer is in opposite direction. It indicates that a current an opposite direction is produced.

(i) Correct symbol for sodium is Na. The symbol of sodium was derived from its latin name “natrium”. 

(ii) Correct name for hydrogen is “H”. The symbol “Hg” is used for mercury.

(iii) Correct symbol for copper is Cu. The symbol “Co” is used for cobalt.

(iv) The given symbol of sulphur (S) is correct.

(v) Correct symbol for calcium is “Ca”. According to IUPAC, the first letter of the symbol is always written as a capital letter (uppercase) and the second letter is always written as a small letter (lowercase). Both letters cannot be written as capital letters.

The weight of iron rod decreases on rusting.

B) X = Na ; Y = CO₃

Electric motors are used in electric fans, refrigerators, mixers, washing machines, etc.

Correct option is d. Na₂CO₃ is neutralized upto the stage of NaHCO₃

Mass of 0.1 cc water = 1 × 0.1 = 0.1 gram

= \(\frac{0.1}{18}\) mol

Thus, number of molecules in one drop of water

= \(\frac{0.1}{18}\) x 6.023 × 10²³

= 0.033 × 10²³ molecules

Correct option is d. NaOH completely and Na₂CO₃ upto the stage of NaHCO₃ are neutralized.

Hydrogen- H, Helium-He, Lithium-Li , Beryllium-Be, Boron-B.

D) neither ‘a’ nor ‘b’