Which of the following molecules does not have a dipole moment? (PPSC 2015)? (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 : c 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. 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
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 (PPSC 2021)? (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
The coldest region of the atmosphere (PPSC 2017) (a) Mesosphere (b) Stratosphere (c) Troposphere (d) Thermosphere Answer: a Video Explanation
Regular use of which of the following fertilizers increases the acidity of soil? (a) Potassium nitrate (b) Superphosphate of lime (c) Ammonium sulphate (d) Urea Answer: c Video Explanation
Find the incorrect statement? (a) BOD value of clean water is less than 5 ppm (b) Drinking water pH should be between 5.5-9.5 (c) carbon, sulphur and nitrogen oxides are the most widespread air pollutants (d) dissolved oxygen concentration below 5 ppm is ideal for the growth of fish Answer: d Explanation Biochemical oxygen demand (BOD) represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic (oxygen is present) conditions at a specified temperature. Video Explanation
Which of the species is not paramagnetic?? (a) As+ (b) Cl– (c) Ne2+ (d) Be+ Answer: b Video Explanation
C-O bond length is minimum in? (a) CO2 (b) CO32- (c) CO (d) all has same Answer: c Explanation Method (1) Bond-multiplicity increases bond-length. Thus, (i) C= ? has least bond-length. (ii) O=C+O? next to C=O. Hence, increasing order of bond-length is CO<CO2?<CO32-? Method (2) (i) More be the value of bond-order smaller be the bond-length and more be the bond-energy. (ii) Bond order (BO)= Total number of bonds associated between two atoms in all structure/ Total number of canonical forms? (a) CO?C=O?BO=13?=3 (b) CO2??O=C=C?BO=24?=2 Hence, order of bond-length CO<CO2?<CO32-? Video Explanation
Which of the following reactions may be associated with aldehyde and ketone? (PPSC 2021)? (a) Nucleophile addition (b) Polymerization (c) Oxidation (d) All of the above Answer: (d) Explanation The nucleophilic addition reaction between hydrogen cyanide (HCN) and carbonyl compounds (generally aldehydes and ketones) results in the formation of cyanohydrins. Base catalysts are often used to increase the rate of the reaction. aldehyde condensation polymer, any of a number of industrially produced polymeric substances (substances composed of extremely large molecules) that are built up in condensation reactions involving an aldehyde. Aldehydes have a proton attached to the carbonyl carbon which can be abstracted, allowing them to be easily oxidized to form carboxylic acids. The lack of this hydrogen, makes ketones generally inert to these oxidation conditions. Nevertheless, ketones can be oxidized but only under extreme conditions. Video Explanation
Sp3d2 hybridization is present in [Co(NH3)63+], find its geometry (PPSC 2020)? (a) octahedral geometry (b) square planar geometry (c) tetragonal geometry (d) tetrahedral geometry Answer: a Video Explanation
For the same value of n, the penetration power of orbital follows the order? (a) s = p = d = f (b) p > s > d > f (c) f < d < p < s (d) s < p < d < f Answer: c Video Explanation
Which of the following statements is incorrect?? (a) I.E.1 of O is lower than that of N but I.E.2 O is higher than that of N (b) Isoelectronic ions belong to the same period (c) The enthalpy of N to gain an electron is almost zero but of P is 74.3 kJ mol-1 (d) none of these Answer: b Video Explanation
Which one will have the highest 2nd ionization energy?? (a) 1s2 2s2 2p4 (b) 1s2 2s2 2p6 3s1 (c) 1s2 2s2 2p6 (d) 1s2 2s2 2p6 3s2 Answer: b Video Explanation
The number of milligrams of KOH required to neutralize the free and combined fatty acid in one gram of a given fat is called? (a) Polenske number (b) Acid number (c) Iodine number (d) none of these Answer: d Explanation The Polenske value (also known as the Polenske number) is a value determined when examining fat. It is an indicator of how much volatile fatty acid can be extracted from fat through saponification. Acid value is the mass of potassium hydroxide in milligrams that is required to neutralize one gram of chemical substance. Iodine no a measure of the unsaturation of a substance (as an oil or fat) expressed as the number of grams of iodine or equivalent halogen absorbed by 100 grams of the substance The saponification value is defined as “the number of milligrams of KOH needed to neutralize the fatty acids obtained by complete hydrolysis of 1gram of an oil sample.” Video Explanation
