Chemistry MCQ Quiz - Objective Question with Answer for Chemistry - Download Free PDF

The correct answer is p block.

Key Points

• The representative elements are the elements placed in the s and p blocks of the periodic table, which include groups 1 to 2 and 13 to 17 (except group 18, the noble gases).
• These elements are reactive due to their partially filled outer electron shells.
• They play a significant role in chemical reactions and are also called main group elements.
• The noble gases (group 18) are not considered representative elements as they have fully filled electron shells and are unreactive.

Additional Information

• The d block elements are called transition metals, and the f block elements are called inner transition metals, including the lanthanides and actinides.
• The transition and inner transition elements exhibit different chemical and physical properties compared to the representative elements.

The correct answer is ​Black.

• The black coating on silver is an example of corrosion.

Key Points

• When a metal deteriorates due to its reaction with air present in the atmosphere, it can be said as corrosion.
• The process of corrosion takes place due to oxidation.
• Iron is rusted and silver is tarnished in the air when they are left free in the air.
• The metals need to be protected from corrosion.
• Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture.
• The beautiful blue-green color (patina) on copper after oxidation is the visible result of the metals losing electrons to the air.

Additional Information

• Many methods are developed via industrial research to protect a metal from corrosion.
• Except for gold and platinum, the corrosion of most of the metals is spontaneous.
• Anti-corrosive chemicals are used to prevent metal from corrosion.
• Iron can also be coated with tin to protect it from corrosion.
• Tin is less reactive and it will protect the iron.
• Cathodic protection, hot deep galvanization, alloyed steel, and barrier coatings are some other methods to protect a metal from corrosion.

The correct answer is gain of oxygen

Concept:

Chemical Reactions:

• A process in which one or more compounds are formed as products completely different from the reacting substances is known as a chemical reaction.
• There is generally a change in heat, colour, or appearance when a chemical reaction takes place.
• The evolution of gas may also occur.
• A chemical reaction may be reversible or irreversible in nature.

Oxidation reaction:

• Oxidation Reaction refers to a reaction in which either the addition of Oxygen takes place or the removal of Hydrogen takes place.
• It can also be said as the process of loss of one or more electrons by atoms or ions.
• Example is:

2Mg + O2 = 2MgO

Reduction Reaction:

• Reduction Reaction refers to a reaction in which either the addition of Hydrogen takes place or the removal of oxygen takes place.

• In the process of reduction, a chemical species also gains electrons.
• It is the reverse of the oxidation reaction.
• Example is:

H2 + F2 → 2HF

Explanation:

Oxidation is a chemical reaction that is characterized by 

• loss of electron
• addition of oxygen atom
• removal of the hydrogen atom 

The substance that undergoes oxidation is said to be oxidized.

The loss of electrons and an increase in the oxidation state are the characteristics of an oxidation reaction.

For example:

H2S + Cl2 → 2HCl + S

In this reaction, the chlorine is getting reduced to hydrochloric acid (HCl) on the addition of hydrogen provided by Hydrogen sulfide (H2S).

The correct answer is 0.

Key Points

• The oxidation number of an oxygen atom in the ozone is zero, just like in oxygen gas. 
• Oxygen being a reactive non-metal occurs in various forms, ozone is also one of the highly reactive gas made up of 3 oxygen atoms.
• Ozone is both natural and a man-made product that occurs in the earth’s upper
• As we know the molecular formula of ozone is O₃, which is 3 oxygen atoms, The atomic number of oxygen is 8 and its valency is -2, as it requires 2 electrons to complete its octet.

Additional Information

• The structure of ozone is

• Now, as we know, the oxidation number is the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom. It is also known as the oxidation state.
• The oxidation number for elements in their natural forms is zero because these compounds are extremely stable.
• The oxidation number represents the number of electrons the element can give away (if positive) or lose (if negative). Such stable molecules have no electrons to lose or gain.
• The oxidation number for O₃ is zero despite being so reactive, which is kind of an exception for this general principle.

Concept:

• When an iron nail gets rusted, iron oxide (Fe2O3) also known as rust is formed.
• During the process of rusting, iron combines with the oxygen molecules from the atmosphere which adds to the weight of iron thus making it heavier.

4Fe + 3O2 → 2Fe2O3 (rust)

Explanation:

• When an iron nail gets rusted, the weight of the nail increases.
• It is because the layer of iron oxide is formed on the surface of the iron nail.
• This iron oxide layer is actually adding oxygen and hydrogen to the nail.

So, the weight of a rusty iron nail is more than the same nail without rusting.

Important Points

• Rusting is an oxidation reaction.
• The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rust. 
• The oxidation process is the loss of electrons during a reaction by a molecule, atom, or ion.
• We can prevent rusting by following methods:
  • Painting
  • Keep moisture at Bay
  • Coat it with Oil, etc.

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:

K2CO3 or potassium carbonate is known as pearl ash.

• Pearl ash, in ancient times, was created by baking potash in a kiln in order to remove impurities. The remaining fine, white powder was pearl ash.
• Potassium carbonate is an inorganic compound and a white salt which is soluble in water.
• It is mainly used in the production of glass and soap.

Additional Information

The correct answer is increases.

Important Points

• In normal cases, the volume of substances increases on heating and decreases while cooling.
• When 1 litre of water is cooled from 4°C to 0°C volume of water will start increasing this due to water's unique property known as 'Anomalous Expansion of Water'.
• Anomalous Expansion of Water occurs between 4°C to 0°C.
• The density of water is a maximum at 4 °C.
• When water is cooled from 4°C to 0°C, its density decreases.
• The anomalous expansion of water helps preserve aquatic life during very cold weather.

Explanation:

• When water reaches 4°C the molecules have been pushed as close to one another as possible and the density of water becomes precisely 1.00 g/cm³
• When water freezes at 0°C due to the crystal structure the molecules arranged in some structured fashion so a little far apart ended up less dense - 0.93 g/cm³  - and so floats due to buoyancy.

As density decreases the volume increases.

Volume = mass /density.

Explanation:

• Calcium hydroxide is sparingly soluble in water producing an alkaline solution known as limewater.
• Calcium Carbonate is a chemical compound found commonly in rocks as minerals and is the main component of pearls and the shells of marine organisms, eggs, etc.
• When carbon dioxide gas is passed through or over limewater, it turns milky due to the formation of calcium carbonate.
• In the chemical reaction it can be shown as :

">Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" id="MathJax-Element-1-Frame" role="presentation" style="display: inline; position: relative;" tabindex="0">">Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" role="presentation" style="display: inline; position: relative;" tabindex="0">Ca(OH)2

• However, when an excess of CO2 ​is passed through this solution, the milkiness disappears. This is due to the formation of calcium bicarbonate which is colorless and soluble in water.

">Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" role="presentation" style="display: inline; position: relative;" tabindex="0">​​Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate

Additional Information Reaction involved-

CaCO₃ + 2HCl →  CaCl₂ + CO₂ + H₂O

• The evolved gas is carbon dioxide which then passes through lime water and turns it milky.

Ca(OH)₂ + CO₂ → H₂O + CaCO₃  

• Due to formation of these compounds
• when excess CO₂ is passed

CaCO₃ + H₂O + CO₂ →  Ca(HCO₃)₂ 

• Bicarbonate is formed which again clears the solution

Mistake Points

•  Do not confuse Calcium carbonate and calcium bicarbonate.
• One produces white colour while the other makes it colourless.

The correct answer is Methanoic acid.

Key Points

• Nettle is an herbaceous plant that grows in the wild.
• Nettle leaves have stinging hair, which causes painful stings when touched accidentally. 
• This is due to the methanoic acid secreted by them. 
• A traditional remedy is rubbing the area with the leaf of the dock plant, which often grows beside the nettle.

Additional Information

The correct answer is The acid present in tomatoes.

Key Points

• Oxalic acid is a chemical compound that occurs naturally in almost every plant to some degree, including fruit, vegetable and grain plants. 
• Tomato contains more than 10 types of acids such as citric acid, malic acid, ascorbic acid, oxalic acid etc. 
• The oxalic acid content of tomatoes is about 50 mg per 100 g serving. 

Additional Information 

• Some natural sources of acid:

The correct answer is option 1, i.e  Alkali Metals.

EXPLANATION:

• The elements in the first group of s-block are also known as Alkali Metals. These have only one electron in their outermost shell and hence are quite reactive as they easily lose their electron to form bonds with non-metals.

• The elements in the second group of s-block are also known as Alkaline Earth Metals. These have two electrons in their outermost shell and are less reactive than Alkali metals.
• Halogens are the group 17 elements and are placed in the p-block.
• Noble gases are the group 18 elements and are placed in the p-block. These are the least reactive amongst all the elements found in the periodic table as they have a stable configuration.

• The word ‘atom’ is coined by Democritus.
• He suggested that if we go on dividing matter at a certain point the atom becomes indivisible or cannot be divided further.
• He called these particles as atoms (Indivisible).

 

Scientist	Discovered
Thomson	Electron
E Rutherford	Discovered alpha and beta particles
John Dalton	Father of Atomic Theory

• The number of water molecules present is washing soda is 10.
• We know the molecular formula for Washing Soda is Na₂CO₃.10H₂O.
• Recrystallisation of Sodium Carbonate (Na₂CO₃) gives washing soda.
• In a Washing soda, water is present in the form of crystals.

The correct answer is Lactic Acid.

Key Points

• Lactic acid is present in Sour milk or curd.
• The sourness of the milk is due to the presence of lactic acid.
• Human beings feel tired due to the accumulation of lactic acid in the muscles.​

Additional Information