Chemistry MCQs for NEET — Practice Questions with Answers

The context states: 'H+ (which is believed to be available from H2CO3 formed due to dissolution of carbon dioxide from air into water.' This indicates that dissolved carbon dioxide contributes indirectly by forming carbonic acid, which then provides the necessary $\text{H}^+$ ions for the cathodic reaction. (Refer to the explanation of the cathodic reaction in iron corrosion).

The text explicitly states: 'In corrosion, a metal is oxidised by loss of electrons to oxygen and formation of oxides.' (Refer to the 'Corrosion' section).

The text lists: 'covering the surface with paint or by some chemicals', 'cover the surface by other metals (Sn, Zn, etc.) that are inert or react to save the object', and 'provide a sacrificial electrode of another metal (like Mg, Zn, etc.) which corrodes itself but saves the object'. While applying an external electric potential might be part of cathodic protection, the specific mechanism of 'applying an external electric potential to make the object cathodic' is not explicitly mentioned as a standalone method in the way the other options are, making it the least directly supported statement from the context. (Refer to the 'Prevention of corrosion' section).

The context states: 'At a particular spot... oxidation takes place and that spot behaves as anode and we can write the reaction Anode: 2 Fe (s) ¾® 2 Fe 2+ + 4 e –'. (Refer to the 'Corrosion' section and the anode reaction equation).

The cathode reaction is explicitly given as: 'Cathode: $\text{O}_2\text{(g)} + 4 \text{H}^+\text{(aq)} + 4 \text{e}^- \longrightarrow 2\text{H}_2\text{O(l)}$'. Thus, water is the primary product of oxygen reduction. (Refer to the detailed explanation of iron corrosion chemistry).

The context states: 'Corrosion slowly coats the surfaces of metallic objects with oxides or other salts of the metal... It causes enormous damage to buildings, bridges, ships and to all objects made of metals especially that of iron.' By converting the metal into oxides or salts, the original metallic properties (strength, integrity) are lost, leading to damage. (Refer to the introductory paragraph about corrosion damage).

The context explains: 'Electrons released at anodic spot move through the metal and go to another spot on the metal and reduce oxygen in the presence of H+'. (Refer to the detailed explanation of iron corrosion chemistry).

The context mentions fuel cells with respect to efficiency improvements and then states: 'Fuel cells are pollution free and in view of their future importance, a variety of fuel cells have been fabricated and tried.' While efficiency is implied, 'pollution free' is the explicit direct advantage mentioned. (Refer to the paragraph before the 'Corrosion' section).

The text explicitly states: 'The chemistry of corrosion is quite complex but it may be considered essentially as an electrochemical phenomenon. At a particular spot... oxidation takes place and that spot behaves as anode... Electrons released at anodic spot move through the metal and go to another spot on the metal and reduce oxygen... This spot behaves as cathode'. This clearly describes an electrochemical cell with distinct anodic and cathodic reactions and electron flow. The objectives section also mentions 'explain corrosion as an electrochemical process'. (Refer to the 'Corrosion' section and 'Objectives').

According to the NCERT text, 'The molecule does not exist for a certain fraction of time in one canonical form and for other fractions of time in other canonical forms.' Instead, the resonance hybrid is a single, unchanging structure that cannot be accurately represented by any single canonical form.