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The correct answer is (a) Oxygen

To EXPLAIN I would say: Oxygen constitutes about 46-47% of the Earth’s CRUST, FOLLOWED by Silicon at 27-28%. Oxygen is predominantly present as a gas in air and several metallic COMPOUNDS that constitute a metal ore (in the form of oxides). Apart from these, Aluminum is the most abundant metal in the Earth’s crust followed by Iron.

Correct option is (b) SE

To ELABORATE: The grey form of Selenium (metallic) and Tellurium consist of PARALLEL CHAINS held by weak metallic bonds. In the presence of light, the weak metallic bonds are excited and as a RESULT, the number of free electrons increases and so does the conductivity. Thus, these elements conduct electricity significantly only in the presence of light. That is why Se and Te are called photosensitive elements.

Right choice is (a) [PCl4]^+[PCl6]^–

For EXPLANATION I would SAY: PHOSPHORUS pentachloride is a pale yellow crystalline solid with a characteristic PUNGENT smell. In the solid state, it exists as an IONIC solid, [PCl4]^+[PCl6]^– in which the cation, [PCl4]^+ is tetrahedral while the anion, [PCl6]^– is octahedral.

The correct answer is (d) White PHOSPHORUS

Easiest explanation: White phosphorus on exposure to LIGHT, it TURNS yellow. It glows greenish in the dark (when exposed to oxygen) and is highly flammable and PYROPHORIC (self-igniting) upon contact with air. Therefore it is called yellow phosphorus.

Right option is (d) Hydrogen

Easiest explanation: The reaction of natural gas and steam is known as the steam REFORMATION of methane. It is an utmost important step in the Bosch-Haber (industrial process to produce AMMONIA), which produces hydrogen gas, H2, ONE of the two reactants ALONGSIDE NITROGEN to produce ammonia in presence of iron catalyst.

The correct option is (a) It is basic in nature

The EXPLANATION: Dinitrogen pentoxide (N2O5), also KNOWN as nitrogen (V) oxide or anhydride of NITRIC acid, is an oxide of nitrogen which is acidic in nature. The oxidation state of nitrogen in it is +5. It exists as a solid below 273K and decomposes to form nitrogen DIOXIDE, nitric oxide and oxygen above a temperature of 273K.

Right answer is (a) Helium

To elaborate: Hydrogen is the lightest and the SMALLEST noble gas, having an ATOMIC number of 2. Owing to its small SIZE and INERT nature, it has the unusual property of diffusing through most commonly used laboratory materials such as RUBBER, glass or plastic.

Correct OPTION is (b) Cl2 > Br2 > F2 > I2

Easiest explanation: Enthalpy of dissociation decreases as the bond distance increases from F2 to I2 due to a corresponding increase in the size of the ATOM as we move down the group from F to I. The F-F bond dissociation enthalpy is, however, smaller than that of Cl-Cl and EVEN smaller than that of Br-Br. This is due to the reason that F atom is very SMALL and HENCE the electron-electron repulsions between the lone pairs of electrons are very large.

The correct choice is (b) 2.75

Easy explanation: pH refers to the power of HYDROGEN ions in the acid solution. It is calculated as the negative logarithm of the concentration of hydrogen ions. In case of 1mM of CONC. sulfuric acid it is FOUND that the concentration of HYDRONIUM ions is 10^-2.75mol dm^-3.

Right answer is (c) It cannot char carbohydrates

Best explanation: Sulphuric ACID is a Lewis acid and is a dense oily liquid which acts as a strong dehydrating agent DUE to its high affinity towards WATER. It chars carbohydrates to from black precipitates of carbon.

The correct choice is (c) 2

Explanation: Basicity of acids refer to the number of H^+ IONS that can be released upon dissolution. In the case of oleum, which is also known as PYRO sulfuric acid, the CHEMICAL formula being H2S2O7, the basicity is 2.

Right option is (d) Potassium permanganate

Explanation: Acidified potassium permanganate is used to test the presence of SO2. A filter PAPER or COTTON wool dipped in acidified KMNO4 is held over the GAS, the former decolorizes, CONFIRMING the presence of gas.

Right choice is (d) Frasch process

The best explanation: Frasch process is the industrial grade process of mining elemental sulfur from UNDERGROUND DEPOSITS. This is done by using pipelines and pumping SUPERHEATED water and causing the MOLTEN sulfur to rise up which is then solidified. It was invented in 1894.

Correct choice is (a) True

The explanation: Although ozone protects us from harmful UV rays, at ground level it is a HIGHLY toxic and IRRITATING gas. It is referred to as a ‘secondary pollutant’ since it is formed from the combination of two primary pollutants, NAMELY nitrogen oxides (NOX) and volatile ORGANIC compounds (VOCS).

The correct choice is (d) Alumina

Explanation: Hall-Heroult process is used to extract aluminum by using an electrolytic cell. Alumina means aluminum oxide. It is dissolved in cryolite, Na3AlF6, to INCREASE electrical CONDUCTIVITY, reduce MELTING POINT and achieve greater yield of aluminum metal.

Correct choice is (d) CO2 and H2O

Best explanation: The reaction show depicts the combustion of ethane. When a HYDROCARBON is burned in excess oxygen it forms carbon dioxide and water. CO represents cobalt and CO represents carbon MONOXIDE.

The correct answer is (d) O > S > Se > TE > PO

To elaborate: Oxygen is the most reactive group 16 ELEMENT. Its reactivity is only SLIGHTLY less than the most reactive elements, halogens. Sulphur is also very reactive particularly at high temperatures which helps in the CLEAVAGE of S-S bonds present in S8 molecules. However, as we move down the group, the reactivity decreases, i.e., O > S > Se > Te > Po.

The CORRECT answer is (d) +4

The explanation: Hypophosphoric ACID, represented chemically as H4P2O6, is an oxoacid of phosphorus. The oxidation state of phosphorus in hypo PHOSPHORIC acid is +4. The two phosphorus atoms in total form 4 single bonds with OH group, two double bonds with OXYGEN and one single bond between the two phosphorus atoms.

The correct option is (b) Red phosphorus

The EXPLANATION is: Like white phosphorus, red phosphorus ALSO EXISTS as P4 tetrahedra but these are joined together through COVALENT bonds to give a polymeric STRUCTURE. Because of polymeric structure, its melting point (883 K) is much higher than that of white phosphorus(317 K).

The correct answer is (B) False

For explanation: White phosphorus is a highly reactive clement and must be stored underwater for safekeeping to prevent it from catching fire spontaneously in the air. In water, white phosphorus reacts with oxygen WITHIN hours or days. In water with low oxygen, white phosphorus may degrade to a highly toxic compound called phosphine, which EVENTUALLY evaporates to the air and is CHANGED to less harmful chemicals.

The correct option is (C) Group 15

To explain: The group 15 of periodic table is better known as the ‘pnicogens’. Pnicogen means ‘to choke’. Since all the elements in this group is choking in nature, including the choking property of NITROGEN. Group 11 does not have a SPECIFIC name; group 13 is REFERRED to as the Boron group. Group 14 is known as the Carbon group.

The correct CHOICE is (C) HOF

The explanation: Hypohalous acids are OXOACIDS in which the hydroxyl group is singly bonded to a HALOGEN. In HOF the hydroxyl group is singly bonded to fluorine making it a hypohalous ACID named hypofluorous acid.

The correct choice is (d) Peroxymonosulfuric acid

For explanation I would say: The CHEMICAL formula of peroxymonosulfuric acid is H2SO5. Popularly known as CARO’s acid, it is widely known for its disinfecting properties. Due to its strong oxidizing property, it is used as the last OPTION to remove any traces of ORGANIC compounds present as impurities.

Right OPTION is (a) It is WEAKLY attracted and loses magnetism on removal of field

Easiest explanation: Oxygen atom is paramagnetic in nature. Meaning, on the application of an EXTERNAL magnetic field, it is slight attracted and loses magnetism on the removal of the field.

Correct OPTION is (b) Fluorine

To ELABORATE: Accounting for only one missing electron, fluorine is highly reactive. Since it NEEDS only one electron to complete its octet, it is the most electronegative element in the periodic table.The DECREASING order of electronegativity is F > CL > O > N.

The correct choice is (b) Oxygen

To elaborate: Oxygen, being a highly electronegative element and reactive tends to react with several substances. These include HYDROGEN and different occurring metals which form compounds. E.g. iron, MAGNESIUM, calcium. NITROGEN is highly unreactive since it bears a TRIPLE BOND and reacts only at high temperatures. Carbon and sulfur are not elements present in air since they are not gases.

Correct option is (d) Oxygen

The explanation is: Oxygen exists as a diatomic gas at ROOM temperature while other elements (S, Se and Te) exist as OCTATOMIC SOLIDS. Due to small SIZE and HIGH electronegativity, oxygen atom forms pπ – pπ double bond with other oxygen atom to form O = O molecule. The intermolecular forces of attraction between oxygen molecules are weak van der Waals forces and hence oxygen exists as a diatomic gas at room temperature.

Right ANSWER is (C) OXYGEN

For explanation I would say: The elements of group 16 have HIGHER values of electronegativity than the corresponding elements of group 15. Actually, oxygen is the second most electronegative element (EN=3.5), the first being fluorine (EN=4.0).

Correct OPTION is (c) PCl3

The best EXPLANATION: Phosphorus pentachloride, when heated, sublimes but decomposes on stronger heating into phosphorus TRICHLORIDE (a colourless pungent-smelling liquid) and chlorine gas.

PCl5 ⇌ PCl3 + Cl2.

Correct answer is (a) True

To explain: PHOSPHORUS trichloride reacts violently with WATER to PRODUCE phosphorus ACID (H3PO3) and HYDROCHLORIC acid.

PCl3 + 3H2O → H3PO3 + 3HCl.

The correct answer is (C) The solution of PHOSPHINE in WATER decomposes in the presence of light

The explanation is: Phosphine is slightly soluble in water and is non-flammable in PURE form. It is a Lewis base and the solution of phosphine in water decomposes in the presence of light giving red phosphorous and HYDROGEN gas.

Correct answer is (C) sp^3d

For explanation: In PCl5, phosphorus undergoes sp^3d HYBRIDIZATION and has trigonal bipyramidal geometry in GASEOUS and liquid STATES. It has three equatorial, P-Cl bonds and two axial, P-Cl bonds. SINCE two axial P-Cl bonds are repelled by three bond pairs while three equatorial bonds are repelled by two bond pairs, therefore, axial bonds are longer than equatorial bonds.

The correct choice is (C) PHOSPHINE is inflammable

The best explanation: Phosphine is a colorless gar with rotten FISH smell and is highly poisonous. In PURE STATE, phosphine is non-flammable but becomes inflammable owing to the presence of P2H4 or White phosphorous (P4) vapours.

Correct answer is (B) Nitric ACID

Easy EXPLANATION: Pickling of stainless steel is the process of removal of a thin layer of the alloyed METAL from the SURFACE. The common reagent used is nitric acid along with calculated amounts of hydrofluoric acid.

The CORRECT answer is (a) Zero

The explanation is: Nitrogen ATOM does not exhibit allotropy. This is because of its relatively small size and high inter-electronic REPULSION due to which the N – N becomes extremely weak. However, theoretically there are TWO predicted forms of allotropes of nitrogen. First, alpha nitrogen assumes a cubic structure and exists only below 35.6 K which is a whooping -237.55°C. Beta nitrogen exists from 35.6 K to 63.15 K. After that, it melts.

Correct option is (d) It is a COLOURLESS gas

The best explanation: Dinitrogen oxide (N2O) or Nitrogen (I) oxide is an oxide of nitrogen where nitrogen has an oxidation state of +1. It is a colourless gas which is neutral in NATURE and which has a sweet ODOUR.

Correct ANSWER is (a) > 0

Explanation: Noble gases have completely filled subshells. As a RESULT, there is no vacant room in their valence shell and hence the additional electron has to be placed in an orbital of the next higher shell. THEREFORE, energy has to be supplied in order to add an electron and so, the electron gain enthalpy of noble gases is positive (> 0).

Right answer is (d) Halogens

Explanation: Fluorine, CHLORINE, BROMINE, iodine and astatine belong to Group 17 of the periodic table. This group is commonly named as Halogens because of their ability to PRODUCE salt on reacting with METALS.

Correct answer is (c) Sulfuryl chloride

To explain I would say: The COMMON name of SO2Cl2 is sulfuryl chloride. Usually, it is confused with thionyl chloride. It is an INORGANIC, colorless liquid with highly pungent odor. It can only be SYNTHESIZED in LABS and not found in nature.

Right choice is (d) WILHELM Scheele

The explanation is: Chlorine was discovered in 1774 by Carl Wilhelm Scheele by HEATING HCl with MnO2. In 1810, DAVY ESTABLISHED its ELEMENTARY nature and suggested the name chlorine on the basis of its colour (Greek, chloros = greenish yellow).

The correct answer is (c) SULFUR

The explanation: Sulfur is the prime vulcanizing agent in rubber and tire industry. Vulcanizing agents are USED to form extensive cross links in NATURAL polymers to increase their strength, durability, elasticity. It is usually added to tire rubber and HEATED to form cross polymer linkages.

Right option is (a) Because of sulfides

To explain: PYRITE is the general name for the mineral ore of sulfur. Two commonly known PYRITES are iron-pyrite, FeS2 and copper pyrite, CuFeS2. They are often termed as FOOL’s gold because of the mineral’s metallic-brass like LUSTER which CLOSELY resembles gold metal.

Correct choice is (a) NO2F

For explanation: Nitrogen dioxide (NO2), also known as nitrogen PEROXIDE or nitrogen (IV) OXIDE, is paramagnetic in nature. So, it reacts with fluorine (F2) and CHLORINE (Cl2) FORMING their respective nitryl compounds. The chemical representation of nitryl fluoride is NO2F.