- 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). - Which species does not contain an sp3-hybridized atom??
(a) BH3
(b) NH4+
(c) NH3
(d) none of these
Answer: (a)
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. - Photochemical smog normally does not contain?
(a) Chlorofluorocarbons
(b) Peroxyacetyl nitrate
(c) Ozone
(d) Acrolein
Answer: (a) - Which of the following molecules does not have a dipole moment? (PPSC 2015)?
(a) CCl4
(b) CH2Cl2
(c) CHCl3
(d) CH3Cl
Answer: (a) - The coldest region of the atmosphere (PPSC 2017)
(a) Mesosphere
(b) Stratosphere
(c) Troposphere
(d) Thermosphere
Answer: (a) - 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) - 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. - Which of the species is not paramagnetic??
(a) As+
(b) Cl–
(c) Ne2+
(d) Be+
Answer: (b) - C-O bond length is minimum in?
(a) CO2
(b) CO32-
(c) CO
(d) all has same
Answer: (c) - 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. - 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)
12. 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)
- 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)
14. 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)
- Gluconeogenesis involves the______. (PPSC 2021)?
(a) synthesis of glycogen from glucose
(b) breakdown of glycogen to form glucose
(c) breakdown of glucose to produce pyruvate
(d) None of the these
Answer: (d)
Explanation
Gluconeogenesis is the pathway by which glucose is synthesized from non-carbohydrate metabolites. The principal gluconeogenic precursors are pyruvate and lactate, certain gluconeogenic amino acids, and glycerol, which is derived mainly from fat metabolism. - Which of the following disaccharides gives two same monosaccharide units on hydrolysis? (PPSC 2021)?
(a) Maltose
(b) Sucrose
(c) Lactose
(d) none of these
Answer: (a)
Explanation
A dissacharide consists of two sugars joined by an O-glycosidic bond. In a dissacharide, two monosaccharides are joined together by acetal or glycoside formation. The hemiacetal OH of one monosaccharide and OH of second monosaccharide dehydrate to establish the bond called glycosidic bond.
Maltose is a disaccharide which is made up of the same monosaccharide units. As you can see in the next figure - Which of the following substance produce acetaldehyde on dry distillation??
(a) (CH3COO)2Ca
(b) (HCOO)2Ca
(c) None of these
(d) Both A and B
Answer: (c) - Which of the following substances does not give iodoform test? (PPSC-2017)
(a) Acetaldehyde
(b) Ethyl alcohol
(c) Acetone
(d) Methyl alcohol
Answer: (d)
Explanation
Iodoform test
Iodoform test is used to check the presence of carbonyl compounds with the structure R-CO-CH3 or alcohols with the structure R-CH(OH)-CH3 in a given unknown substance. The reaction of iodine, a base and a methyl ketone gives a yellow precipitate along with an “antiseptic” smell. - Which of the following compounds will react with Tollen’s reagent?
(a) CH3-CHO
(b) CH3-CH-CH3
(c) CH3-COOH
(d) CH3-CO-CH2-CH3
Answer: (a)
Explanation
Tollens test
Tollens test is generally given by compounds having aldehydic group (aldehydes,alpha-hydroxy ketones and formic acid-its -COOH behaves like a aldehydic group). It gives a white ppt of Silver (where the silver salt is reduced to silver metal and the aldehyde is oxidised to silver salt of carboxylic acid. - In which of the following methods are liquid samples injected into the column in gas chromatography? (PPSC 2021)
(a) Gas tight syringe
(b) Micro-syringe
(c) Rotary sample valve
(d) None of these
Answer: (b)
Explanation
A microsyringe is used to inject the sample through a rubber septum into a flash vaporizer chamber at the head of the column. The sample vaporizes to form a mixture of carrier gas, vaporized solvent and vaporized analytes.
Gas tight syringes are ideal for dispensing both liquids and gases. They have a precision-machined PTFE plunger tip which creates a leak-free seal. With the tight fit, the tip essentially wipes the interior of the syringe barrel free of sample.
Gas and liquid sampling valves are most frequently used to sample gases or liquids in constantly flowing streams such as those in chemical reactors, chemical transfer lines, natural gas processing, and fermenters.
