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Correct choice is (a) True

To elaborate: EXTRACTIVE METALLURGY is a process of conversion of metal IONS from the COMPOUNDED STATE to metal atoms in the elemental state, whereas the corrosion occurs by the conversion of metal atoms into metal ions.

The correct option is (c) HEXAGONAL close packed structure

The explanation is: HCP is ABBREVIATED as hexagonal close packed structure. CONDITIONS for HCP is a1=a2≠a3 and α=β=60, γ̈=120, where a1, a2, a3 are unit vectors in THREE directions and α, β, γ̈ are ANGLES between them. Magnesium possesses an HCP crystal structure.

Correct option is (a) True

The explanation: In PRACTICAL cases, the corrosion rate is ESTIMATED based on the current density generated. We KNOW that the current density increases with the increase in oxidizer concentration and passivity will only be achieved when the current density CROSSES critical current density value (IC).

The correct CHOICE is (b) Cathodic diffusion control

For explanation I would say: Concentration polarization is ALSO called as cathodic diffusion control. Concentration polarization is controlled by the diffusion of ions from the BULK solution to the metal electrolyte INTERFACE. This diffusion can be accelerated by agitation or by increasing the velocity of the solution.

Right option is (d) Activation, Concentration and Resistance polarization

The EXPLANATION: Polarization is the potential difference occurred DUE to the non-equilibrium conditions, due to the change in concentration or TEMPERATURE. These are classified into three types. They are i) Activation polarization ii) Concentration polarization III)Resistance polarization.

Correct answer is (d) Use of corrosion-resistant material and REGULAR inspection

The best I can explain: MAINTENANCE and operating costs are the preventive measures in ORDER to avoid the plant shutdowns and catastrophic accidents. Plant shutdowns USUALLY cost 5-10 TIMES more than the maintenance and operating costs.

The CORRECT option is (a) True

The best explanation: We can’t differentiate grain and grain boundaries in a non-etched POLISHED sample. ETCHANT (a chemical) is used to react with the grain boundaries in ORDER to reveal grain and grain boundaries.

The correct option is (b) dry corrosion

The best EXPLANATION: Dry corrosion occurs in the ABSENCE of moisture usually by vapors and gases whereas the wet corrosion, galvanic corrosion and CREVICE corrosion occurs in aqueous STATE or in the PRESENCE of moisture.

Right choice is (d) Insulating dissimilar METALS and selection of CLOSE metal combinations in a galvanic series

Explanation: The galvanic EFFECT is due to the contact of TWO dissimilar metals in a conductive solution. It can be minimized by insulating dissimilar metals with non-conductive MATERIALS. And it can be reduced by the selection of close metal combinations in a galvanic series.

Right answer is (a) E^ocathode-E^oanode

The explanation is: A ELECTROCHEMICAL CELL consist of two electrodes with a potential difference preferentially one acts as a CATHODE and other as an anode. The standard state of each specific electrode is constant and it measured against the HYDROGEN electrode at 25°C and 1 atm pressure. And standard cell potential is calculated as E^ocathode-E^oanode.

Right choice is (a) Absorption

Easiest EXPLANATION: DRY corrosion occurs in the absence of a LIQUID phase. Vapors and gases are usually the corrodents. These will hit and adsorbed on the metal surface to form corrosion. So dry corrosion can be explained by an absorption mechanism.

Right ANSWER is (C) WAGNER’s THEORY

Easy explanation: Wagner’s theory states that the oxidation of metal is electrolytic in nature and the RATE of oxidation is determined by the electrical properties of the corrosion product.

The correct answer is (c) Both Thermodynamics and Electrochemistry

Easiest explanation: Thermodynamic studies and calculations indicate the spontaneous direction of the reaction. The thermodynamic stability of CORROSION PRODUCT is relatively higher than reactant. Whereas the electrochemistry DEALS with ELECTRODE kinetics of the reaction.

The correct choice is (d) Metals, Non-metals, Ceramics, Plastics and Rubbers

Best EXPLANATION: Corrosion is defined as the destruction or deterioration of a MATERIAL because of reaction with its ENVIRONMENT. Every material in the universe will undergo corrosion but it VARIES in time and form. Any PHYSICAL, Chemical or Mechanical deviation of the original material is known as Corrosion.

Correct OPTION is (a) True

Easiest explanation: Case1 (OXYGEN-free acids)

Anodic reaction: M==M>^+n+ne

Cathodic reaction: 2H^++2e==>H2

Case2 (OXYGENATED acids)

Anodic reaction: M==>M^+n+ne

Cathodic reaction: 2H^++2e==>H2, O2+4H^++4e==>2H2O

This oxygen REDUCTION increases the cathodic rate which CORRESPONDINGLY increases the anodic rate or corrosion rate.

Correct choice is (d) both OXIDATION and reduction

Explanation: Corrosion is an electrochemical reaction. It occurs by THERELEASE and GAIN of electrons from various species which are TERMED as oxidation and reduction respectively. It can be observed with change in the oxidation state of the species.

Right choice is (c) Both BHOPAL tragedy and crude oil leak in Canada

To explain I would say: Bhopal gas tragedy is caused by the immediate flow of water into Methyl ISOCYANATE gas tank. This resulted in the formation of much carbon dioxide and the TEMPERATURE INSIDE the tank reach over 200°C. Crude oil leakage in Canada occurred in 2017, occurred DUE to corrosion at the sealing.

Correct option is (c) Includes active and passive potentials of a metal

Best explanation: Galvanic series is the ARRANGEMENT of various engineering materials (pure metals and ALLOYS) in a decreasing reduction potential value in seawater. Galvanic series is more ACCURATE than EMF series and it can be measured at various temperatures of a specific MEDIUM. It includes the active state potential and passive state potential of a metal.

Right option is (a) True

Best explanation: Electrode with relatively HIGH reduction potential preferentially ACT as a cathode and the other electrode will act as an anode. The effect of galvanic coupling can be MINIMIZED by selecting metal COMBINATIONS with less potential DIFFERENCE.

Right choice is (d) Fe in H2SO4

The best I can explain: IRON in SULFURIC acid, the corrosion rate of iron increases at first and then it decreases with an increase in corrosive concentration. This is because, at low concentrations, iron will DISSOLVE in sulfuric acid whereas at high concentrations it forms a PASSIVE layer on the sample surface.

The CORRECT answer is (a) True

Easy explanation: If two dissimilar metals are placed in contact with each other in a conductive electrolyte, the potential difference produces ELECTRON flow between them. This results in the acceleration of preferential ANODE dissolution. This is KNOWN as the effect of Galvanic coupling.

The correct answer is (b) False

To elaborate: Though ice is the solid FORM of water but it doesn’t conduct electrons. The FUNCTION of an ELECTROLYTE is to transfers ions from one electrode to another. Thus, given STATEMENT is false. Corrosion needs an anode, a cathode and a CONDUCTIVE electrolyte.

Correct answer is (a) FCC=HCP>BCC

The best explanation: Packing EFFICIENCY = (VOLUME of ATOMS in unit cell/volume of the unit cell)*100. Packing-efficiency of FCC, HCP, and BCC is 74%, 74%, and 68%. Therefore, the correct ORDER is FCC=HCP>BCC.

Correct option is (b) 18Cr-8Ni in H2SO4+Fe^+3

Best explanation: Initially corrosion rate of Stainless steel (18Cr – 8Ni) in sulfuric acid increases with an increase in the CONCENTRATION of ferric ion (Fe^+3). And then it is followed by a rapid DECREASE in corrosion rate due to the formation of a passive LAYER. Critical current density (ic) must be achieved to UNDERGO the TRANSITION from active to passive.

Right answer is (a) Loss of reactivity

Explanation: Passivation is the state of metal in which stable films or barriers are FORMED. These stable films obstruct the contact of CORROSIVE MEDIUM to the metal surface. Most of the engineering metals undergo passivation under DIFFERENT atmospheric conditions.

Right answer is (d) Temperature, HUMIDITY and conductance of the corroding MEDIUM

Easy explanation: The main factors that AFFECT the rate of corrosion includes the EFFECT of pH, temperature, humidity, conductance of the corroding medium, oxygen concentration, presence of IMPURITIES. These factors are based on the nature of environment.

The CORRECT CHOICE is (a) MDD

The explanation: Uniform corrosion is the corrosion that occurs throughout the entire exposed surface of a metal and it is uniform in depth of corrosion LAYER. Weight loss METHOD I.e. MDD is used to know the EXTENT of uniform corrosion.

Correct ANSWER is (B) Corrosion is a non-SPONTANEOUS process

The explanation is: Corrosion is a spontaneous process which results in DEGRADATION of materials and it is irreversible in nature. Spontaneous reaction is a reaction which results in the formation of stable products from unstable without need of any EXTERNAL energy.

The correct option is (C) 2FE(OH)3

The best EXPLANATION: +3 oxidation state of iron is more STABLE state of iron than +2 oxidation state. The REACTION is follows as

Fe+H2O+½O2==>Fe(OH)2

2Fe(OH)2+H2O+1/2O2==>2Fe(OH)3.

Correct choice is (b) FE==>Fe^+2+2e, O2+2H2O+4e==>4OH^–

The explanation is: Iron dissolution (ANODIC reaction) Fe==>Fe^+2+2e. Oxygenated hydrogen reaction (cathodic reaction) in a NEUTRAL solution (pH=7) is O2+2H2O+4e==>4OH^–.

Right option is (d) To predict the life time and to compare the corrosive resistant of materials

To EXPLAIN: CORROSION rate expression is USED to quantify the corrosion process. This helps US to predict the life time of a component and to compare with different materials. This also helps us to change the process VARIABLES in order to decrease the corrosion rate.

Correct option is (c) contamination caused by lead

The explanation: Lead exposure is a public health hazard as it causes development effects in INFANTS and YOUNG children. Lead contamination in drinking WATER is the most CONTRIBUTOR of lead exposure to humans. To avoid exposure, various steels such chromium steels and coated steels are being used for this purpose.

Right answer is (a) True

For explanation: Oxides of CARBON, Sulphur and nitrogen on REACTING with rain water, forms DILUTE acids. These acids on REACTION with the marble of Taj mahal degrades its appearance, hence it is regarded as corrosion. Acid rains also accelerates the natural corrosion and EROSION.

Correct choice is (a) MPY

Explanation: Pitting CORROSION involves LOSS of metal at the selected spots on the surface of a metal. It PENETRATES into VARIOUS depths based on the CONCENTRATION of corrosive medium and nature of metal. MPY measures penetration range.

Correct choice is (d) Standard hydrogen electrode and a CALOMEL electrode

The best I can explain: In EMF series all metals are referenced against the hydrogen electrode (H2/H+) which is arbitrarily DEFINED as zero. This is known as the Standard hydrogen electrode (SHE). The SATURATED calomel electrode also acts as a reference electrode based on the reaction between elemental mercury (Hg) and mercury(I) chloride (Hg2Cl2). And the electrode POTENTIAL value of the calomel electrode is +0.241 V.