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The correct answer is Sodium carbonate.

Explanation:

• Washing soda is a chemical compound with the formula Na2CO3, known as sodium carbonate, and it's a salt of carbonic acid.
• Properties of a Washing soda:
• It is a transparent crystalline solid.
• It is one of the few metal carbonates which are soluble in water.
• It is alkaline with a pH level of 11, it turns red litmus to blue.
• It has detergent properties or cleansing properties because it can remove dirt and grease from dirty clothes, etc.
• It attacks dirt and grease to form water-soluble products, which are then washed away on rinsing with water.

Important Points

Some common chemical compounds with their common names are:

The correct answer is 7.

Key Points

• The pH value of salts of strong acid and strong base is 7.
• The salts are from a strong acid and strong base do not hydrolyze and the resulting salt pH will remain 7.
• The anion in the salt form's strong base does not attract the H+ from the water.

Additional Information

• Salt of a strong acid and a weak base is acidic with a pH value less than 7 because acid is strong which retains the pH value less than 7.
• Salt of a weak acid and strong base is base with a pH value of more than 7 because the base is strong hence pH of the whole solution will be more than 7.
• Salt of a strong acid and strong base is neutral because both are strong and cancels strong effects of each other, the pH will be 7.

An amphoteric compound is a molecule or ion that can react both as an acid and as a base.

• Examples of Amphoteric oxides are aluminium oxide(Al2O3) and zinc oxide(ZnO).

Additional Information

• Na2O, Sodium oxide is a simple strongly basic oxide.
• K2O, Potassium oxide is a basic oxide.
• CaO, Calcium oxide is a basic oxide because it dissolves in water to form calcium hydroxide.

The Correct Answer is Nitrogen.

Key Points

• Nitrogen is used during the packaging process to exclude and remove air and prevent oxidation.
• Oxygen is highly-reactive and it combines with other molecules, which results in food spoiling or losing its' freshness.

Important Points

Rancidity

• Rancidity, condition produced by aerial oxidation of unsaturated fat present in foods and other products which gives unpleasant odor or flavor.
• When a fatty substance is exposed to air, its unsaturated components are converted into hydroperoxides, which break down into volatile aldehydes, esters, alcohols, ketones, and hydrocarbons.
• This gives out bad smell.

Concept: -

Chemical change a change in which one or more new substances are formed is a chemical change.

• A chemical change occurs when the substance's composition is changed.
• When bonds are broken and new ones are formed a chemical change occurs.
• Examples of Chemical change are the bursting of a firecracker, the germination of seeds, and coal formation from buried trees.

Physical changes only change the appearance of a substance.

• Physical changes are limited to changes that result in a difference in the display without changing the composition.
• The boiling of water is an example of Physical change.

Explanation: - 

Ripening of fruit. burning of coal, and curling of curd all are non-reversible changes that involve a change in the chemical composition of a substance and hence are Chemical Changes.

Whereas, evaporated water can be recovered back by condensation, and water's chemical composition in both the liquid phase and vapor phase are the same.

Hence, evaporation is a physical change and not a chemical change.

So, the correct option is (3).

The correct answer is nitrous oxide and sulphur dioxide.

• Definition of Acid Rain - Rain or any other form of precipitation that has a higher level of hydrogen ions (i.e. low pH < 5.6), is termed as Acid Rain.
• Oxides of sulphur and nitrogen which are acidic in nature are responsible for causing Acid Rain.
• Human activities like the burning of fossil fuels, volcanic activities, etc. result in the formation of sulphur dioxide and nitrogen oxides.
• These oxides after oxidation and reaction with water are the major contributors to Acid Rain.
• Following chemical reactions occur:

1. 2SO₂ (g) + O₂ (g) + 2H₂O (l) → 2H₂SO₄ (aq)
2. 4NO2 (g) + O2 (g) + 2H2O (l) → 4HNO₃ (aq)

Aftermaths of Acid Rain:

1. Deteriorates plant and animal life in the aquatic ecosystem.
2. It corrodes water pipes resulting in the leaching of heavy metals (iron, lead, copper) into drinking water.
3. It damages buildings and other structures made of metal or stone (eg. Taj Mahal)
4. Chemical reaction occurring at the surface of Taj Mahal: CaCO₃ + H2SO4 → CaSO₄ + H2O + CO₂

• ​

Important Points

• The term Acid Rain was first coined by Scottish chemist Robert Angus Smith in the year 1852.
• Normal rainwater is weakly acidic due to the presence of carbonic acid, which is formed due to the absorption of carbon dioxide from the atmosphere.

The correct answer is Hydrogen.

Key Points

• When a metal is put in acid, it gets smaller and smaller as it gets used up in the chemical reaction.
• At the same time, bubbles of gas can be seen. The bubbles produced in the reaction are hydrogen gas.
• This can be proven using a burning splint because hydrogen is flammable.
• Metal + acid → salt + hydrogen
• Hydrochloric acid + magnesium → magnesium chloride + hydrogen.

Additional Information Characteristics of a base:

• Bases are bitter in taste and have a slippery texture.
• When a base reacts with an acid, a salt is formed.
• A base turns the color of a red litmus paper into blue color.

 The reaction of a base with a metal:

• When a base reacts with a metal, it involves the formation of salt along with the liberation of hydrogen gas.
• Some metals react with a base to form salts and hydrogen gas.
• When aluminum metal is heated with sodium hydroxide solution, the sodium aluminate and hydrogen gas is formed. Zinc metal also reacts with sodium hydroxide solution to form hydrogen gas.
• All the metals do not react with bases to form salt and hydrogen.

The correct answer is CaSO4.1/2 H2O.

​EXPLANATION:

• Plaster of Paris (POP) is a quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry.
• It is also known as the Plaster of Paris because for the preparation of POP, the abundant gypsum was first found near the capital city of France i.e. Paris.
• The chemical formula of the Plaster of Paris is CaSO4.\(\frac{1}{2}\) H2O. Therefore option 3 is correct.
• Application of Plaster of Paris is as follows

1. It is used as a building material as a protective coating on walls and ceilings.
2. It is used as a moulding and vesting agent for decorative elements.
3. It is also used for aesthetic touch to the construction elements.
4. It is also used as plaster in orthopaedics and as a filling material by dentists, etc.

Mistake Points

\(\begin{array}{*{20}{c}} {CaS{O_{4.}} + \frac{1}{2}{H_2}O + 1\frac{1}{2}{H_2}O}\ {\left( {Plaster,Of,Paris} \right)} \end{array} \to \begin{array}{*{20}{c}} {CaS{O_4}.2{H_2}O}\ {\left( {Gypsum} \right)} \end{array}\)

• Gypsum is an ore of Calcium (Ca). The chemical formula of Gypsum is CaSO4. 2H2O.
• Gypsum is mainly used as a fertilizer, as the main constituent in plaster, chalk, etc.
• The plaster of Paris on mixing with water produces gypsum.
• Calcium Sulphate Hemihydrate (CaSO4·1/2 H2O) on hydration leads to the crystallization of gypsum calcium sulphate dihydrate (CaSO4·2H2O).

The process in which the system and surroundings can be restored to the initial state from the final state without producing any changes in the thermodynamic properties of the universe is called a reversible process.

If the system and its surroundings cannot return to their initial states at the end of the reversed process, this process is an irreversible process.

The correct answer is Neutralisation.

Key Points

 Neutralization:

• Neutralization reactions can be defined as chemical reactions in which an acid reacts with a base to produce a salt along with water.
• The reaction of an acid with a base is called a neutralization reaction.
• For example, the reaction of hydrochloric acid(HCI) with sodium hydroxide (NaOH) produces a solution of sodium chloride(NaCl) (salt) and some additional water molecules.
• The neutralization of a strong base and strong acid has a pH equal to 7.
• The neutralization of a strong base and weak acid will be greater than 7.
• The neutralization of a strong acid and weak base will be less than 7.

Additional Information

 Decomposition reactions:

• It can be defined as a reactant compound, which breaks down into two or more products.
• Many decomposition reactions happen all around us i.e. electrolysis of water to produce oxygen and hydrogen, and the decomposition of carbonic acid in soft drinks.
• Decomposition reactions can be either endothermic or endothermic.

 Combination reactions:

• It is the opposite reaction of decomposition reactions in which two reactant molecules react to give one product.

 Reduction:

• It is the process of gaining or losing electrons or removing or adding hydrogen atoms to a molecule.
• Product oxidant + e- The amount of oxidant has decreased.