Chemistry

211. Atomic mass of an element is equal to the sum of number of

Atomic mass of an element is equal to the sum of number of

[amp_mcq option1=”electrons and protons only” option2=”protons and neutrons only” option3=”electrons and neutrons only” option4=”electrons, protons and neutrons” correct=”option2″]

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The correct answer is (B) protons and neutrons only. The atomic mass of an element (more accurately, the mass number of a specific isotope or the relative atomic mass) is primarily determined by the mass of the particles in the nucleus. Protons and neutrons are located in the nucleus and account for almost all of an atom’s mass. The mass of electrons is negligible in comparison.
The nucleus of an atom contains protons and neutrons, which contribute significantly to its mass. Electrons have very little mass.
The Mass Number (A) of an isotope is the sum of the number of protons (Z) and neutrons (N) in its nucleus (A = Z + N). The atomic mass listed on the periodic table for an element is the weighted average of the masses of its naturally occurring isotopes, taking into account their relative abundances.

212. Which one of the following is the most fundamental characteristic of a

Which one of the following is the most fundamental characteristic of an element ?

[amp_mcq option1=”Melting point” option2=”Atomic number” option3=”Colour” option4=”Atomic weight” correct=”option2″]

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The correct answer is (B) Atomic number. The atomic number (Z) of an element is defined as the number of protons in the nucleus of an atom of that element. This number is unique to each element and determines its fundamental chemical identity.
The atomic number is the defining characteristic of an element, determining its position in the periodic table and its chemical properties.
Melting point and color are physical properties that can vary depending on conditions or even within different forms (allotropes) of the same element. Atomic weight (more precisely, relative atomic mass) is the weighted average mass of isotopes of an element and is determined by the number of protons and neutrons, but the identity is fixed by the number of protons alone.

213. How many covalent bonds are present in a Chloropropane molecule having

How many covalent bonds are present in a Chloropropane molecule having molecular formula, C₃H₇Cl ?

[amp_mcq option1=”6″ option2=”8″ option3=”9″ option4=”10″ correct=”option4″]

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The correct answer is (D) 10. The molecular formula is C₃H₇Cl. This represents a chloropropane molecule, which is derived from propane (C₃H₈) by replacing one hydrogen atom with a chlorine atom. Let’s consider the structure of propan-1-ol (CH₃-CH₂-CH₂-Cl) or propan-2-ol (CH₃-CHCl-CH₃). Counting the single covalent bonds:
In CH₃-CH₂-CH₂-Cl:
C1-H (3 bonds)
C1-C2 (1 bond)
C2-H (2 bonds)
C2-C3 (1 bond)
C3-H (2 bonds)
C3-Cl (1 bond)
Total = 3 + 1 + 2 + 1 + 2 + 1 = 10 covalent bonds.
In CH₃-CHCl-CH₃:
C1-H (3 bonds)
C1-C2 (1 bond)
C2-H (1 bond)
C2-Cl (1 bond)
C2-C3 (1 bond)
C3-H (3 bonds)
Total = 3 + 1 + 1 + 1 + 1 + 3 = 10 covalent bonds.
A covalent bond is formed by the sharing of electron pairs between atoms. To find the total number of covalent bonds in a simple organic molecule, you need to count all the single, double, and triple bonds between atoms.
In organic molecules, carbon typically forms 4 bonds, hydrogen forms 1 bond, and chlorine forms 1 bond. By drawing the skeletal structure and adding hydrogens to satisfy valency, one can systematically count the bonds.

214. Which one of the following statements is NOT correct ?

Which one of the following statements is NOT correct ?

[amp_mcq option1=”Buckminsterfullerene is an allotrope of carbon” option2=”Diamond is a good conductor of electricity” option3=”Graphite is a good conductor of electricity” option4=”In graphite, each carbon atom is linked to three other carbon atoms” correct=”option2″]

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The statement which is NOT correct is (B) Diamond is a good conductor of electricity. Diamond has a structure where each carbon atom is bonded to four other carbon atoms via strong covalent bonds. All valence electrons are tightly held in these bonds, meaning there are no free electrons to carry charge. Therefore, diamond is a poor conductor of electricity (a good electrical insulator).
Electrical conductivity in materials depends on the presence of free charge carriers, such as free electrons. The arrangement and bonding of atoms determine the availability of these carriers.
Statement (A) is correct: Buckminsterfullerene (C60) is a form of carbon, belonging to the fullerene family, which are allotropes of carbon. Statement (C) is correct: Graphite conducts electricity because each carbon atom is bonded to three others, leaving one delocalized electron per atom that can move throughout the layers. Statement (D) is correct: In graphite, carbon atoms are arranged in hexagonal layers where each carbon is covalently bonded to three other carbon atoms.

215. Vinegar is also known as

Vinegar is also known as

[amp_mcq option1=”ethanoic acid” option2=”nitric acid” option3=”sulphuric acid” option4=”tartaric acid” correct=”option1″]

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Vinegar is primarily an aqueous solution of acetic acid, which is also known by its IUPAC name, ethanoic acid.
– Acetic acid (CH₃COOH) is a weak organic acid.
– Culinary vinegar typically contains 5% to 8% acetic acid by volume.
– Acetic acid is produced industrially and also biologically by the fermentation of ethanol by acetic acid bacteria.
– It is widely used in cooking, as a preservative, and for cleaning purposes.

216. The number of maximum electrons in N Shell is

The number of maximum electrons in N Shell is

[amp_mcq option1=”2″ option2=”8″ option3=”18″ option4=”32″ correct=”option4″]

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According to the rules governing electron shells, the maximum number of electrons in the N shell (n=4) is 32.
– Electron shells are designated by principal quantum numbers (n), starting from n=1 for the innermost shell (K shell).
– The formula for the maximum number of electrons that can occupy a shell with principal quantum number ‘n’ is 2n².
– For the N shell, n=4.
– Applying the formula 2n² for n=4: Maximum electrons = 2 * (4)² = 2 * 16 = 32.
– The distribution of electrons in shells follows specific rules, filling the lower energy shells first, but the maximum capacity is given by 2n².

217. Chalk and marble are different forms of

Chalk and marble are different forms of

[amp_mcq option1=”Calcium hydrogen carbonate” option2=”Calcium carbonate” option3=”Calcium acetate” option4=”Sodium carbonate” correct=”option2″]

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Chalk and marble are both naturally occurring forms of calcium carbonate (CaCO₃).
– Calcium carbonate is a common substance found in rocks as the minerals calcite and aragonite.
– Marble is a metamorphic rock composed primarily of recrystallized carbonate minerals, most commonly calcite.
– Chalk is a soft, white, porous sedimentary rock, a form of limestone composed primarily of the mineral calcite.
– While chemically the same (CaCO₃), chalk, limestone, and marble differ in their crystal structure, formation process, and physical properties like hardness and texture.
– Calcium carbonate is also the main component of shells of marine organisms, snails, and eggshells.

218. Which one of the following is the major constituent of biogas ?

Which one of the following is the major constituent of biogas ?

[amp_mcq option1=”Carbon dioxide” option2=”Nitrous oxide” option3=”Methane” option4=”Oxygen” correct=”option3″]

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The correct option is C) Methane.
Biogas is a mixture of gases produced by the breakdown of organic matter in the absence of oxygen, primarily consisting of methane and carbon dioxide.
The typical composition of biogas is about 50-75% methane (CH4) and 25-50% carbon dioxide (CO2), with traces of other gases like hydrogen sulfide, nitrogen, and hydrogen. Methane is the primary combustible component that gives biogas its fuel value.

219. Which one of the following represents the correct order of electron re

Which one of the following represents the correct order of electron releasing tendency of metals ?

[amp_mcq option1=”Zn > Cu > Ag” option2=”Ag > Cu > Zn” option3=”Cu > Zn > Ag” option4=”Cu > Ag > Zn” correct=”option1″]

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The correct option is A) Zn > Cu > Ag.
The electron releasing tendency of metals is determined by their position in the electrochemical series or reactivity series. Metals higher in the series have a greater tendency to lose electrons and act as reducing agents, thus having higher electron releasing tendency.
The reactivity series orders metals based on their decreasing reactivity: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au. Zinc is higher in the series than copper, and copper is higher than silver. Therefore, the order of electron releasing tendency is Zn > Cu > Ag. This also corresponds to their relative standard electrode potentials (standard reduction potentials, where less positive or more negative potential indicates higher electron releasing tendency).

220. Which one of the following is not a monatomic element ?

Which one of the following is not a monatomic element ?

[amp_mcq option1=”Copper” option2=”Helium” option3=”Iodine” option4=”Barium” correct=”option3″]

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The correct answer is C) Iodine.
A monatomic element is an element that exists stably as individual atoms rather than in molecules composed of two or more atoms. Helium (He) is a noble gas and exists as single atoms, making it monatomic. Copper (Cu) and Barium (Ba) are metals that exist as lattices of individual atoms in their solid state. Iodine (I) is a halogen that exists as a diatomic molecule ($I_2$) in its standard solid state and gaseous state (when it sublimes). Thus, Iodine is not a monatomic element; it is diatomic.
Noble gases (He, Ne, Ar, Kr, Xe, Rn) are the most common examples of naturally occurring monatomic elements. While metals exist as individual atoms in their solid structure, the term “monatomic” is most frequently used to contrast with diatomic or polyatomic molecular elements like $O_2$, $N_2$, $S_8$, $P_4$, and halogens ($F_2$, $Cl_2$, $Br_2$, $I_2$). Among the given options, Iodine is the only one that exists as a diatomic molecule in its elemental form.
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