Class 10 Science Chapter 4 MCQ

The general formula of alkyne is CnH2n-2 where, n is the number of carbon atoms. The first member of Alkyne homologous series is ethyne C2H2.

A carbon atom has 4 electrons in its outermost shell, so it requires 4 more electrons to achieve the stable, 8-electron inert gas electron arrangement, which it gets by sharing. Since one carbon atom requires 4 electrons to achieve the eight-electron inert gas structure, therefore, the valency of carbon is 4. That is, carbon is tetravalent (tetra = four; valent = valency).

In saponification reaction, when an ester is heated with sodium hydroxide solution, ester gets hydrolysed (breaks down) to form the parent alcohol and sodium salt of carboxylic acid.

The two common allotropes of carbon, diamond and graphite, have entirely different physical properties. For example, diamond is extremely hard whereas graphite is soft; diamond is a non-conductor of electricity whereas graphite is a good conductor of electricity.

Here, all these statements are correct. Hence, your answer will be option [D].

Due to its softness, powdered graphite is used as a lubricant for the fast moving parts of machinery. Since graphite is non-volatile, it can be used for lubricating those machine parts which operate at very high temperatures (where ordinary oil lubricants cannot be used). Graphite can be used as a dry lubricant in the form of graphite powder or mixed with petroleum jelly to form graphite grease. Graphite powder can also be mixed with lubricant oils.

When a small piece of sodium reacts with ethanol, a colourless solution of sodium ethoxide, CH3CH2ONa is obtained. It also gives off bubbles of hydrogen gas. Sodium ethoxide is known as an alkoxide. You can easily understand by this equation: C2H5OH + 2Na → 2C2H5O-Na+ + H2

Though oxides of carbon (like carbon monoxide and carbon dioxide), carbonates, hydrogen carbonates and carbides are also carbon compounds but they are not considered to be organic compounds. This is because their properties are very different from those of the common organic compounds.

Pentane has 16 covalent bonds.

The property of carbon element due to which its atoms can join with one another to form long carbon chains is called catenation. So, it is the property of “catenation” of carbon element which is responsible for a very large number of organic compounds (catenation means “self-linking”).

The general formula of alkynes is CnH2n – 2 where n is the number of carbon atoms in one molecule of the alkyne. You can easily understand by this example: Example, If an alkyne has 3 carbon atoms in its molecule, then n = 3, and its molecular formula will be C3H2×3–2 or C3H4.

A hydrocarbon in which the two carbon atoms are connected by a “double bond” or a “triple Bond” is called an unsaturated hydrocarbon. Propene, CH3CH = CH2 and Propyne CH3 –C ≡ CH both have double and triple bonds, respectively hence unsaturated. Propane and chloropropane are saturated hydrocarbons which contain only single bonds.

A soap molecule is made up of two parts: a long hydrocarbon part and a short ionic part -COO-Na+ group. The long hydrocarbon chain is hydrophobic (water repelling) and ionic portion is hydrophilic (water attracting).

Here, all these statements are correct. Hence, your answer will be option [D].

Oils are unsaturated compounds containing double bonds. Addition reaction are characteristic property of unsaturated hydrocarbons. The given reaction is an example of addition reaction. You can easily understand by this: Edible oils + H2 + Ni or Pd + Heat → Fats (ghee)

Here, all the statements are correct. Hence, your answer will be option [D].

KMnO4 acts as oxidizing agent because it removes hydrogen from CH3CH2OH and adds one oxygen to it. Note: Oxidizing agent is a substance which gives oxygen to the compound for oxidation (i.e. oxygen is removed from it) or which removes hydrogen from the compound. In other words, we can say that CH3CH2OH is oxidised to CH3COOH in the presence of oxidising agent like KMnO4.

It is the characteristics of a “Homologous Series” is that all the members of a homologous series can be represented by the same general formula. For example, all the members of the alkane series can be represented by the general formula CnH2n+2.

A molecule of ammonia (NH3) has only single bonds and these are covalent bonds. Note: Atomic number of N is 7. Its electronic configuration is 2, 5 so it needs 3 more electrons to complete its “Octet”. It gains 3 electrons each from 3 hydrogen atoms. Also, N has one lone pair of electrons. The pair of electrons on the nitrogen atom in NH3 molecule which is not involved in bond formation is called lone pair.

It is the characteristics of a Homologous Series is that the difference in the molecular masses of any two adjacent homologous is 14 u. For example, the molecular mass of methane (CH4) is 16 u, and that of its next higher homologue ethane (C2H6) is 30 u. So, the difference in the molecular masses of ethane and methane is 30 – 16 = 14 u.

Carbon mainly forms covalent compounds, which due to the absence of free ions, are generally poor conductors of electricity. Also, the forces of attraction in between their molecules are weak. Note: Atomic number of carbon is 6. So, its electronic configuration is 2, 4. It can achieve the inert gas electron arrangement only by the sharing of electrons.

Carbon exist in the atmosphere in the form of carbon dioxide gas (CO2) in air (only 0.03%). Carbon also occurs in the earth’s crust in the form of minerals like carbonates. It also occurs in the form of fossil fuels, organic compounds, wood, cotton and wool etc.

The common name of pentanone is methyl propyl ketone.

Here, all these statements are correct. Hence, your answer will be option [D].

Here, 14 u, will be the differences in the molecular formulae and molecular masses in all these statements. Hence, your answer will be option [D]. You can easily understand by this: In option [A]: The difference in the molecular formulae of CH3OH and C2H5OH is CH2. The difference in the molecular masses of CH3OH and C2H5OH is 46 – 32 = 14 u. In option [B]: The difference in the molecular formulae of C2H5OH and C3H7OH is CH2. And the difference in the molecular masses of C2H5OH and C3H7OH is 60 – 46 = 14 u. In option [C]: The difference in the molecular formulae of C3H7OH and C4H9OH is CH2. And the difference in the molecular masses of C3H7OH and C4H9OH is 74 – 60 = 14 u.