Kpk Chemistry 2020 — Solved MCQs

Question 1

The rate of reaction _ as reaction proceeds.

Accepted Answer

D. Decreases — The rate of reaction decreases as the reaction proceeds. This is because, as reactants are used up, their concentration diminishes, which in turn slows down the reaction rate. Here’s a simple way to remember this concept:Rate of Reaction ∝ 1​/Concentration of Reactants

Question 2

Surface tension has. _ unit.

Accepted Answer

A. Nm-1 — Surface tension is typically measured in Newtons per meter (N/m) in the International System of Units (SI).

Question 3

The splitting of spectral lines In the presence of magnelic fleld is called _.

Accepted Answer

B. Zeeman effect — The splitting of spectral lines in the presence of a magnetic field is known as the Zeeman Effect. This effect is due to the distortion of the electron orbitals because of the magnetic field. The atomic energy levels, and the transitions between these levels, are influenced by a magnetic field. The pattern and amount of splitting are a signature that a magnetic field is present, and of its strength.

Question 4

Maximum number of electrons in a subshell with l = 2and n = 3 is:

Accepted Answer

D. 10 — The maximum number of electrons in a subshell is given by the formula: 4l+2So, substituting l=2 into the formula, we get: 4(2)+2 =10So, a subshell with l=2 (which corresponds to a d subshell) can hold a maximum of 10 electrons.The principal quantum number n=3 doesn’t affect the maximum number of electrons in a subshell, but it does indicate that we’re talking about the 3d subshell.

Question 5

Enthalpy is heat content of a system at constant _.

Accepted Answer

A. Pressure — Enthalpy is the heat content of a system at constant pressure. It’s a state function that’s used in many thermodynamic processes. In other words, the enthalpy of a system is the amount of energy it has that can be used to do work, plus the product of its pressure and volume. The formula for enthalpy (H) is given by: H=U+PVThis concept is particularly important in processes where pressure is held constant, such as in chemical reactions happening in open containers, where the system is exposed to atmospheric pressure.

Question 6

In ethyne for the formation of R (x) bonds _ orbitals are involved.

Accepted Answer

A. sp hybridized — In ethyne (also known as acetylene), which has the chemical formula C2​H2​.In total, three orbitals are involved in the formation of the triple bond in ethyne: one sp-hybrid orbital for the sigma bond and two p-orbitals for the pi bonds.

Question 7

Kp=kc, when Δn is equal to:

Accepted Answer

A. Zero — The equilibrium constants Kp and Kc are equal when Δn equals 0.Here, Δn is the difference in the sum of the stoichiometric coefficients of the products and reactants from a balanced chemical equation. In other words, Δn is calculated as follows: Δn=∑(products)−∑(reactants)So, when the number of moles of gaseous products is equal to the number of moles of gaseous reactants (i.e., Δn = 0), Kp equals Kc.

Question 8

Evaporation of Liquid causes _.

Accepted Answer

C. Cooling — Evaporation of a liquid causes cooling. This is because evaporation is a process that requires energy. When molecules of a liquid escape and turn into gas (evaporate), they take this energy from the remaining liquid, which results in a decrease in temperature. This is why you might feel cool when water on your skin evaporates. It’s the same principle that makes sweating an effective way for our bodies to cool down.

Question 9

Limiting reactant is one which _.

Accepted Answer

B. Consumes earlier — The limiting reactant is the substance that is completely consumed in a chemical reaction. It determines or limits the amount of product that can be formed in the reaction. Once the limiting reactant is used up, the reaction cannot continue, even if other reactants are still available.

Question 10

Freezing point of soluton as compare to the pure solvent is:

Accepted Answer

B. Lower — The freezing point of a solution is lower than the freezing point of the pure solvent. This is a phenomenon known as freezing point depression.When a solute is added to a solvent, it interferes with the ability of the solvent molecules to form a regular pattern in the solid state, which is why more energy must be removed (lower temperature) for the solution to freeze.

Question 11

A larger value of Kc means that at equilbrium:

Accepted Answer

A. Less reactants and more products — A larger value of Kc (the equilibrium constant) means that at equilibrium, the concentration of the products is greater than the concentration of the reactants.In other words, the reaction tends to favor the product side. This is because Kc is defined as the ratio of the concentrations of the products to the concentrations of the reactants, each raised to the power of their stoichiometric coefficients.So, if Kc is large, it means the numerator (concentration of products) is much larger than the denominator (concentration of reactants), indicating that the reaction proceeds mostly to the right to form products.

Question 12

In BF the bond angles are _.

Accepted Answer

C. 120° — In BF (Boron Fluoride), the bond angles are 120°. This is because BF has a trigonal planar molecular geometry, which means the three atoms are all in the same plane and at equal distances from each other, forming an equilateral triangle. This results in bond angles of 120°.

Question 13

In SI units, the value of "R" is:

Accepted Answer

A. 8.3413 Nmk-1mol-1 — The value of the gas constant R in Newton is 8.31432×10^3 N⋅m⋅k−1mol−1. This value is used when the pressure is measured in Newtons per square meter (N/m² or Pa), volume in cubic meters (m³), amount of substance in kilomoles (kmol), and temperature in Kelvin (K).

Question 14

Which one of the fotlowing is paramagnetic?

Accepted Answer

B. O2+2 — Paramagnetism is a form of magnetism whereby some materials are attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, diamagnetic materials are repelled by magnetic fields and form induced magnetic fields in the direction opposite to that of the applied magnetic field.Paramagnetic materials have at least one unpaired electron in their electron configuration, which is the source of their magnetic behavior.In the case of O2+2, it has unpaired electrons, making it paramagnetic.

Question 15

If 10% urea is present in NaCl as impurity, its crystal will become _.

Accepted Answer

A. Cubic — The presence of urea as an impurity in NaCl promotes the formation of octahedral NaCl crystals. So, among the options present, the shape of the NaCl crystals would be closest to a cubic structure.

Question 16

Example of a buffer solution is _.

Accepted Answer

C. CH3COOH/CH3COONa — This is a classic example of a buffer solution. CH3COOH (acetic acid) is a weak acid and CH3COONa (sodium acetate) is its conjugate base. The acetic acid can donate protons (H+) to the solution, while the sodium acetate can accept protons. This allows the solution to resist changes in pH.

Question 17

_ has no units.

Accepted Answer

C. Mole fraction — Mole fraction (X) is the ratio of the number of moles of a component to the total number of moles of all components in the mixture. It is a dimensionless quantity and therefore, has no units. It only represents a ratio, so it’s just a number.

Question 18

Oxidation take place at _.

Accepted Answer

A. Anode — Oxidation takes place at the anode. In an electrochemical cell, the anode is the electrode where oxidation (loss of electrons) occurs.

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