CBSE 11TH CHEMISTRY - Online Test
Q1. Ionization enthalpy increases across a period because
Answer : Option C
Explaination / Solution:
Consider moving from lithium to fluorine across the second period, where successive electrons are added to orbitals in the same principal quantum level. The shielding of the nuclear charge by the inner core of electrons does not increase very much to compensate for the increased attraction of the electron to the nucleus. Thus, across a period, increasing nuclear charge outweighs the shielding. Consequently, the outermost electrons are held more and more tightly and the ionization enthalpy increases across a period.
Q2. According to Pauli’s exclusion principle
Answer : Option A
Explaination / Solution:
The Pauli Exclusion Principle states that, in an atom or molecule, no two electrons can have the same four electronic quantum numbers. As an orbital can contain a maximum of only two electrons, the two electrons must have opposing spins.
Q3. Recycling of materials and energy will lead to :
Answer : Option C
Explaination / Solution:
Recycling of materials and energy will lead to decrease in environmental pollution as amount of waste material will be lesser and so lesser pollution will be caused.
Q4. The number of moles of solute present in 1 kg of solvent is called--------------.
Answer : Option D
Explaination / Solution:
Molality is defined as no. of moles of solute present per kg of solvent.It is denoted as " m " . Mathematically ,
Molality (m)
= [ number of moles of the solute ] / kg of solvent
Since , this mode of expressing the strength of a solution involves ( weight / weight ) relationship of solute and solvent , the molality of the solution is not affected by variation in temperatures of the solution.
Q5. Water behaves as an amphoteric substance because
Answer : Option A
Explaination / Solution:
An amphoteric compound is a compound that can act either as an acid, or as a base in a chemical reaction.
A first example of water's amphoteric character is the fact that it can self-ionize to a small extent. A water molecule is capable of donating one of its protons (H+) to a neighbouring water molecule, forming the hydroxyde and hydronium ions.
Q6.
In , molecule below the dipole moment is zero although the B- F bonds are oriented at an angle of to one another. Net dipole moment in molecule is
Answer : Option A
Explaination / Solution:
BF3 has symmetrical structure in which the three B-F bonds are oriented at an angle of 120° to one another. Also the three bonds lie in one plane and the dipole moments of these bonds cancel one another giving net dipole moment equal to zero.
Q7. lithium halides are somewhat covalent because
Answer : Option D
Explaination / Solution:
Smaller is the size, greater is the polarization . so more is the covalent character.
Q8.
If an – functional group is present in an organic compound it is called amine. If a functional group is present in an organic compound then it is called
Answer : Option C
Explaination / Solution:
is amide functional group.
Q9. Surface tension decreases as the temperature is raised because
Answer : Option D
Explaination / Solution:
Surface tension decreases as the temperature is raised because Increase in temperature increases the kinetic energy of the molecules and effectiveness of intermolecular attraction decreases.
Q10. The solutions which resist change in pH on dilution or with the addition of small amounts of acid or alkali
Answer : Option C
Explaination / Solution:
The solutions which resist change in pH on dilution or with the addition of small amounts of acid or alkali are called Buffer Solutions. Buffer solutions of known pH can be prepared from the knowledge of pKa of the acid or pK b of base and by controlling the ratio of the salt and acid or salt and base. A mixture of acetic acid and sodium acetate acts as buffer solution around pH 4.75 and a mixture of ammonium chloride and ammonium hydroxide acts as a buffer around pH 9.25.X`
