- Which of the following atoms or ions has the electronic configuration 1s22s22p63s23p6 ?
(a) Ne
(b) Al3+
(c) Cl-
(d) Mg2+
Answer: c
Explanation
The Chlorine (17) electron configuration will be 1s22s22p63s23p5. The chloride ion (Cl-), on the other hand, has an additional electron for a total of 18 electrons. Following Aufbau Principle, the electron occupies the partially filled 3p subshell first, making the 3p orbital completely filled. The electronic configuration for Cl- can, therefore, be designated as 1s22s22p63s23p6.
Video Explanation - Which of the following contains an atom (other than hydrogen) which lacks an octet of valence electrons?
(a) NH3
(b) H3O+
(c) NH4+
(d) BH3
Answer: d
Explanation
The presence of d-orbitals, which can accommodate up to ten electrons, makes this possible. The only possibility for boron is to bond to three hydrogen atoms, in which case it forms a compound (borane, BH3) that does not fulfill the octet rule.
Video Explanation - Which of the following molecules does not have a dipole moment?
(a) CCl4
(b) CH2Cl2
(c) CHCl3
(d) CH3Cl
Answer: a
Video Explanation - Which of the following compounds has an ionic bond?
(a) H2O
(b) NH4Cl
(c) CH3Li
(d) all of these
Answer: b
Explanation
NH4Cl is an inorganic compound with the chemical name Ammonium Chloride. It is also called Sal ammoniac, the salt of ammonia and hydrogen chloride. Ammonium chloride helps maintain pH and exerts a mild diuretic effect.
In the NH4Cl molecule, an ionic bond is formed between NH4+ and Cl– ions
3 covalent bonds are formed between N and three H atoms.
One coordinate bond is formed between N and one H atom.
CH3Li
The formula for this compound can be written as [CH3-][Li+] because the metal is very electropositive compared to the carbon atom (if we look at their electronegativities, C = 2.5, Li = 1.0). The [CH3-] group, a methyl anion, has covalent bonds between carbon and hydrogen.
water (H2O) is a covalent compound.
Because the bond forms between two hydrogens and one oxygen are covalent in nature. The covalent bond is formed due to the sharing of an electron that occurs between hydrogen (H) and oxygen (O) atoms in order to complete their octet shell and hence, attains stability.
Video Explanation - Which of the following elements is the most electropositive?
(a) B
(b) C
(c) Cl
(d) N
Answer: a
Explanation
“Electropositivity can be defined as the tendency of an atom to donate electrons and form positively charged cations.” Electropositivity is primarily exhibited by metallic elements, especially the alkali metals and the alkaline earth metals.
Electropositivity is known to increase down groups and decrease across periods in the modern periodic table (i.e., electropositivity decreases from left to right and it increases from up to down).
Video Explanation - Which of the following bonds is the most polar?
(a) C-H
(b) O-H
(c) C-O
(d) N-H
Answer: b
Video Explanation - Which species does not contain an sp3-hybridized atom?
(a) BH3
(b) NH4+
(c) NH3
(d) none of these
Answer: a
Explanation
The observed structure of the borane molecule, BH3, suggests sp2 hybridization for boron in this compound. The molecule is trigonal planar, and the boron atom is involved in three bonds to hydrogen atoms . All others have sp3 hybridization.
Video Explanation - Which of the following statements is wrong?
(a) When two orbitals overlap in-phase with each other, a bonding molecular orbital forms.
(b) When two orbitals overlap out-of-phase with each other, an antibonding molecular orbital forms.
(c) When one of two atoms connected by a σ bond rotates about the bond axis, orbital overlap is lost.
(d) When one of two atoms connected by a π bond rotates about the bond axis, orbital overlap is lost.
Answer: C
Video Explanation - Which of the following statements is wrong?
(a) Hydroboration-oxidation of a terminal alkyne gives a ketone as the main product.
(b) Hydrogenation of an internal alkyne over the Lindlar catalyst gives a cis alkene .
(c) In the epoxidation of an alkene with a peroxy acid, the peroxy acid is electrophilic.
(d) none of these
Answer: a
Explanation
a. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
b. A less efficient catalyst, Lindlar’s catalyst permits alkynes to be converted to alkenes without further reduction to an alkane. Lindlar’s Catalyst transforms an alkyne to a cis-alkene because the hydrogenation reaction is occurring on the surface of the metal.
C. The epoxidation reaction is where an alkene is subjected to a peroxyacid to convert it into an epoxide. Another way to say it is epoxidation is the electrophilic addition of oxygen to the double bond of the alkene.
Video Explanation
- Which of the following reaction is not shown by ketones?
(a) Reaction with HCN
(b) Reaction with NaHSO3
(c) Reaction with 2 4 dinitrophenyl hydrazine
(d) Reaction with Fehling solution
Answer: D
Explanation
What is Fehling’s test?
One of the most popular tests used for the estimation or detection of reducing sugars and non-reducing sugars is the Fehling’s test. The test developed by German chemist H.C. Von Fehling is also used to differentiate between ketone functional groups and water-soluble carbohydrates.
Video Explanation - Find the incorrect statement for a nucleophile
(a) A nucleophile is a Lewis acid
(b) Nucleophiles do not seek electron
(c) Ammonia is a nucleophile
(d) Nucleophiles attack low electron density sites
Answer: a
Video Explanation - Which among the following is the most deactivating meta-directing group in aromatic substitution reaction?
(a) -COOH
(b) -SO3H
(c) -NO2
(d) -CN
Answer: c
Video Explanation - Which of the following statements is wrong?
(a) The main orbital interactions in the transition state of an electrophilic addition to an alkene are between the LUMO of the electrophile and the HOMO of the alkene.
(b) The lower the LUMO of the electrophile, the more reactive it is.
(c) The lower the HOMO of the alkene, the more reactive it is.
(d) none of these
Answer: C
Video Explanation - What will be the value of ΔH, if the forward and reverse reactions have the same energy of activation?
(a) ΔH = ΔG = ΔS = 0
(b) ΔS = 0
(c) ΔG = 0
(d) ΔH = 0
Answer: d
Explanation
Hint: Change in enthalpy for a reaction equal to change in activation energies.
For a reaction, the change in enthalpy depends on the change in activation energies of the product and reactants.
We can write it as,ΔH=(Ea)f−(Ea)b
Here,
(Ea)f denotes the activation energy for forward reaction
(Ea)b denotes the activation energy for backward reaction
According to question, (Ea)f=(Ea)b
Therefore, ΔH=(Ea)f−(Ea)b=0
ΔH=0
Video Explanation - What is the function of a catalyst in a chemical reaction?
(a) decrease rate constant of reaction
(b) increases activation energy of reaction
(c) reduces enthalpy of reaction
(d) does not affect the equilibrium constant of reaction
Answer: d
Video Explanation - Which is true for the entropy of a spontaneous reaction?
(a) ΔS(system) – ΔS(surroundings) > 0
(b) ΔS(system) + ΔS(surroundings) > 0
(c) ΔS(surroundings) > 0 only
(d) ΔS(system) > 0 only
Answer: b
Video Explanation - Photochemical smog normally does not contain
(a) Chlorofluorocarbons
(b) Peroxyacetyl nitrate
(c) Ozone
(d) Acrolein
Answer: a
Video Explanation - Formalin is _ % solution of formaldehyde in water
(a) 10%
(b) 20%
(c) 40%
(d) 60%
Answer: C
Explanation
Methanal or formaldehyde is soluble in water, alcohol and ether. Its 40% aqueous solution is marketed as formalin.
Video Explanation - Find the secondary pollutant among these
(a) PAN
(b) N2O
(c) SO2
(d) CO2
Answer: a
Video Explanation - Alum’s capacity to purify water is due to
(a) softens hard water
(b) pathogenic bacteria get destroyed
(c) impurities’ coagulation
(d) it improves taste
Answer: c
Video Explanation
