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Right option is (d) Helium

Easy EXPLANATION: Noble GASES can form compounds in which the gases are entrapped in the cavities of crystal lattices. Such compounds are CALLED clathrates. Only ARGON, Krypton, XENON and Radon are known to form clathrates among the noble gases.

The correct choice is (B) O2 and He

The best I can explain: Helium-Oxygen (80:20 or 70:30) mixture provides a dramatic benefit for asthma patients with severe EXACERBATIONS. Helium is about 10% as dense as ROOM air and, consequently, travels more EASILY down narrowed PASSAGES.

Correct OPTION is (c) HClO4> HClO3 > HCLO2

The explanation is: ACIDIC strength of OXOACIDS of the same halogen increases with increase in the oxidation number of the halogen. The oxidation number of halogens in HClO4, HClO3 and HClO2 is 7, 5 and 3 so the Acidic strength of HClO4 is greatest followed by HClO4 and HClO2.

Right choice is (c) H3O^+ + Cl^–

To elaborate: The hydrogen chloride molecule, HCl DISSOCIATES in water GIVING rise to one hydrogen ion and a chloride ion. The extremely small hydrogen ion BEARING the positive charge is instantly ATTRACTED by the unshared pair of electrons of the oxygen atom in water molecules, consequently giving rise to the hydronium ion, H3O^+.

The correct choice is (d) BrO4^– > IO4^– > ClO4^–

Explanation: Perhalates are strong OXIDIZING AGENTS, their oxidizing power DECREASES in the order: BrO4^– > IO4^– > ClO4^–. This can be explained on the basis of their electrode potentials. Although among perhalates BrO4^– is the strongest oxidizing AGENT, yet it is WEAKER oxidizing agent than F2.

The correct choice is (a) True

Easiest EXPLANATION: FLUORINE atom is extremely small COMPARED to chlorine. This means that the bond of H – F is much more polar than that of H – Cl, CAUSING the H atom to be more tightly bonded in case of H – F than in H – Cl. Since hydrogen chloride is able to release the H+ much easily, the latter is a stronger ACID.

Correct answer is (a) True

Explanation: Group 17 ELEMENTS are called halogens. The name halogen (Greek, halo = sea salts, genes = producing) meaning sea salt formers was GIVEN to them by Schweigger in 1811 because the salts (chlorides, BROMIDES and IODIDES) of the first three elements occur in sea water.

Right choice is (b) Fluorine

For explanation I would say: Of all the HALOGENS, fluorine is the most reactive and hence is ALSO called super halogen. Fluorine is also the most electronegative (EN = 4.0) element in the periodic table. This INDICATES that fluorine has a high tendency to gain electrons from other elements with LOWER ELECTRONEGATIVITIES.

Correct choice is (c) sp^3

Best explanation: The hybridization of SULPHUR in SULPHURIC acid is sp^3 and is tetrahedral shaped. The structure is often DRAWN with TWO double BONDS, with double bond formed from d-orbitals on Sulphur and p-orbitals on oxygen.

Correct answer is (B) Burning of Sulphur or roasting sulphide ores to GENERATE SO2

The best explanation: The first step involved in FORMING sulphuric acid through contact process is Burning of Sulphur or roasting sulphides ores to generate SO2. Sulphur dioxide is purified by removing dust and arsenic IMPURITIES.

Correct answer is (C) Pyrosulfuric ACID

The explanation: In the first step, sulfur is converted to sulfur dioxide. Second step involves reacting it with more oxygen to form sulfur trioxide. INSTEAD of reacting sulfur trioxide with water to form sulfuric acid directly, an alternative, safer METHOD is utilized to dissolve sulfur trioxide gas in sulfuric acid to form OLEUM, also known as pyrosulfuric acid.

The correct choice is (C) Sulfur dioxide

To elaborate: Sulfur dioxide was USED as a refrigerant before CFCs. This is due to its CHARACTERISTIC features bearing high HEAT of evaporation and ability to be easily condensed.

The CORRECT option is (a) SO2

The best explanation: Sulfur dioxide is the most commonly known OXIDE of sulfur, which occurs naturally and can be prepared in labs too. Industrially, it is an essential gas to produce a variety of CHEMICALS involving SO2 as the CHIEF component. For e.g. contact process for PRODUCING sulfuric acid.

Correct answer is (d) Red PHOSPHORUS

The explanation: Alpha-black phosphorus is the most STABLE ALLOTROPE of black phosphorus. Alpha-black phosphorus is produced from red phosphorus. When red phosphorus is HEATED in a sealed tube at 803 K, it forms alpha-black phosphorus.

The correct choice is (a) 1

For explanation I would say: The nitrogen ATOM in NH3 (ammonia) bears one lone PAIR of electron. Each single electron of hydrogen is bonded to the nitrogen atom. THREE of out five electrons of nitrogen are involved in bonding whereas the unbounded two electrons MAKE up the single unshared pair of electron.

The CORRECT answer is (d) Carbon tetrachloride

The best I can explain: In PRESENCE of SUNLIGHT, a free radical substitution reaction takes place between the reacting methane and chlorine molecules where in each elementary reaction a hydrogen atom is replaced by a chlorine atom in the new product. First, methane converts to 1-chloromethane which in TURN produces DICHLOROMETHANE followed by tri-chloromethane and tetra-chloromethane, respectively.

Correct answer is (a) True

Easy explanation: The main commercial source of helium is natural gas which mainly CONTAINS HYDROCARBONS ALONG with varying AMOUNTS of carbon dioxide, nitrogen, HYDROGEN sulphide and helium (2-7%).

The correct option is (a) True

Best explanation: Sulphur dioxide is purified by removing DUST and arsenic impurities. Arsenic is a catalyst POISON for vanadium PENTOXIDE catalyst. Hence, it has to be REMOVED completely before entering into the catalytic CHAMBER.

Correct choice is (b) Sulfuric acid

Explanation: Sulfuric acid is commonly used in industrial CHEMICAL manufacturing as a reactant or a laboratory reagent. The FORMULA is H2SO4. It is one of the most powerful oxidizing and dehydrating agents in the chemical field and finds a number of APPLICATION, such as production of FERTILIZERS and DYES and many more.

Correct option is (C) Selenium

Explanation: Selenium has eight allotropic forms, of which three are RED monoclinic forms CONTAINING Se8 rings. The thermodynamically most STABLE form is grey hexagonal metallic Selenium which consists of polymeric helical chains.

Right answer is (d) Volcanoes

The explanation: Elemental sulfur is PREDOMINANTLY found near volcanic CRATERS. This is because the sulfur dioxide released from the craters condenses to form liquid sulfur. This then SOLIDIFIES to form elemental sulfur. In soil and OCEANS, sulfur is USUALLY found in the form of pyrites.

Correct choice is (a) ns^2np^4

Easiest explanation: The elements of group 16 have six electrons in the VALENCE shell and HENCE their general OUTER electronic configuration is ns^2np^4. The four p-electrons are arranged in three p-orbitals as px^2py^1pz^1 in accordance with Hund’s RULE.

Right ANSWER is (b) False

Best explanation: The ammonia molecule has the capability to FORM a dative BOND due to the LONE pair of electrons. There is a formation of H-bond due to strong dipole-dipole attraction between ammonia and water molecules where as in phosphine the H-bond is weak and the P-H bond is non-polar so, it is only slightly SOLUBLE in water but highly soluble in non-polar solvents.

The correct CHOICE is (d) Pungent

To elaborate: AMMONIA has a highly pungent smell. With a sharp, pinching smell, it causes SEVERE irritation in the nose and throat. This pungent smell of ammonia is used as a means to identify the presence of ammonium CATION, NH4^+ in SALT analysis.

Right option is (d) Ostwald’s process

The explanation is: Ostwald’s process is the name of the industrial process to manufacture nitric acid in bulk. It involves the oxidation of ammonia which forms nitric oxide. This is then reacted with more OXYGEN to produce NITROGEN dioxide. Subsequently, nitrogen dioxide is dissolved in water to produce adequate concentrations of nitric acid. Contact process is used to produce sulfuric acid. Solvay is used to OBTAIN sodium CARBONATE and Haber-Bosch to obtain ammonia.

Correct option is (a) True

The BEST I can explain: Nitrogen monoxide or Nitrogen(II) oxide or nitric oxide is a very reactive compound due to the PRESENCE of an odd ELECTRON(paramagnetic nature). It instantly REACTS with oxygen to FORM nitrogen dioxide.

The correct answer is (b) Blue

The BEST I can explain: Dinitrogen trioxide (N2O3) is FOUND to be blue in colour in both its liquid and solid state. The blue colouration tends to appear because dinitrogen trioxide is a radical pair of nitric OXIDE and NITROGEN dioxide that tend to absorb strongly in the visible region to appear bright blue.

Correct option is (c) Black PHOSPHORUS

The explanation is: Black phosphorus is thermodynamically, the most stable ALLOTROPE of phosphorus and does not burn in air even up to 673 K. It has a sharp MELTING point of 860 K. Like GRAPHITE, it is fairly a good conductor of electricity.

Right choice is (c) NaNO3 + H2SO4 → NAHSO4 + HNO3

For EXPLANATION I would say: The most appropriate lab scale preparation method of nitric acid, HNO3 is using an alkali nitrate salt and react it with concentration nitric acid in a glass retort.Nitrous acid being highly unstable DECOMPOSES into nitric acid. The other two sets of REACTION represent the industrial process of MANUFACTURING nitric acid i.e. Ostwald’s process.

Correct option is (c) Platinum-Rhodium gauze

To elaborate: AMMONIA is oxidized to nitrogen (II) OXIDE in the PRESENCE of Pt/Rh gauze catalyst at a temperature of 500 K and a pressure of 9 bars. The NITROUS oxide is then converted to nitrogen dioxide which is further reacted with water to produce nitric acid. The NO FORMED is recycled.

Correct ANSWER is (d) Four

For explanation: Covalency of an atom refers to the number of electrons that atom can share to form chemical BONDS. Usually it is the number of bonds formed by the atom. In CASE of nitrogen, its atom can share up to four electrons, one in the s-subshell and the other three in the p-subshell. In ADDITION to this, absence of d-orbitals restricts its covalency to four only.

Right answer is (d) Absence of VACANT d-orbitals

Explanation: Nitrogen shows ANOMALOUS properties compared to other elements of GROUP 15 because of the absence of vacant d-orbitals. In addition to this, anomalous properties are a result of nitrogen ATOM’s smaller size, highest electronegativity and highest ionization ENERGY with respect to all the elements in group 15.

The correct option is (c) Planar

Easy explanation: In the gas state, the nitric acid MOLECULE has a triangular planar SHAPE with a steric number of 3 no lone pairs of electron. There are two major RESONANCE forms of nitric acid.

Right option is (b) NITRIC oxide

Easy explanation: Car ENGINES release only nitric oxides. Nitrogen and oxygen from the air combine at HIGH temperatures in the engine to produce nitrogen (II) oxide by the reaction N2(g) + O2(g) → 2NO(g). Nitric oxides rise in the atmosphere and are oxidized to nitrogen dioxide, NO2 which DISSOLVES in the precipitating water to form acid RAIN.

Correct choice is (c) It is an inert gas

Easy explanation: Gases like argon is also nontoxic. However, nitrogen gas is still the most preferred since it eliminates all the possibilities of unwanted oxidation and explosions. In the WELDING industry this prevents metals from CORRODING. Nitrogen is USED in the food industry for PACKAGING since it PROVIDES a pressurized atmosphere that reduces package collapse.

Right answer is (d) NO3^–

To explain: The brown RING test is used to DETERMINE the presence of nitrate IONS, NO3^–. Dilute ferrous sulfate SOLUTION is added to solution CONTAINING nitrate ion. Following this, concentrated sulfuric acid is added along the sides of the test tube. A brown ring is formed at the junction concentrated sulfuric acid and solutions.

The correct option is (d) The N – N single bond is weaker and unstable

Explanation: The N – N single bond is highly weak and unstable due to high magnitude of inter-electronic repulsions of non-bonding electrons which in turn is CAUSED by the single bond’s small bond length. As a RESULT the catenation tendency BECOMES weaker due to the MENTIONED factors leading to INSTABILITY.

Correct option is (a) AMMONIA

Explanation: The primary product of Haber-Bosch PROCESS is ammonia, NH3. In this process, N2(g) and H2(g) are reacted at a high temperature of 700 K and 200 atm pressure in presence of iron-bed catalysts. It is an exothermic process which takes PLACE in accordance with Le Chatelier’s principle. Nitric acid is produced by Ostwald’s process. Nitrous acid is produced by reacting sodium nitrite with a mineral and pyridine by Chichibabin process.

Right choice is (b) Size decreases

Easiest explanation: The size of the atoms of the elements decrease from left to right in the same period. Considering the row to be the same, the electrons are added to the same shell. HOWEVER, the INCREASE in atomic number reflects the increase in number of protons i.e. the positive charge. Hence, the overall effective NUCLEAR charge increases. Consequently, the electron CLOUD is pulled even more closer to the nucleus of the atom. Therefore, the size decreases.

Correct answer is (C) (n-2)F^0(n-1)d^0 ns^2np^1-6

Explanation: The general configuration representation of p-block elements is (n-2)f^0(n-1)d^0ns^2np^1-6. This is because the s-subshell is completely FILLED, whereas, the p-subshell contains at least 1 electron. Other options are ruled out since EITHER or both d – and f – subshell are PARTIALLY filled.

Correct option is (a) NaNO2

Easy explanation: NaNO2, sodium nitriteis the only convenient compound that can be used to OBTAIN free nitrogen, EVEN in laboratories. Sodium nitrite can be REACTED with ammonium chloride, both in aqueous form, producing NaCl and nitrogen, N2 along with water and small traces of HNO3 and NO.

Correct answer is (c) 3

For explanation I would say: With five ELECTRONS in its outer most shell, it needs three more electrons to have a complete shell CONSISTING of eight electrons which is the noble electronic configuration. The ion formed by the nitrogen atom is N^3-. It ATTAINS the electronic configuration on neon.

Correct choice is (d) Nitrogen (IV) oxide

Explanation: Treating COPPER chips with CONCENTRATED nitric acid releases toxic BROWN gas, NO2, nitrogen (IV) oxide. It is a reddish-brown gas with pungent odor.

Right answer is (c) 2

Best explanation: The nitrogen atom has two stable isotopes: ^14N and ^15N, 99.6% and 0.4% (by mass) respectively. There are ALSO fourteen known RADIOISOTOPES with one ADDITIONAL nuclear isomer.