Q23. Iron is polymorphic and can exist in different structures at different temp
ID: 292124 • Letter: Q
Question
Q23. Iron is polymorphic and can exist in different structures at different temperatures. Which of the following is NOT true at atmospheric pressure? A At room temperature iron is a body-centred cubic structure called ferrite B Above 912 °C iron transforms to face-centred cubic austenite ? Above 1 394°Ciron transforms to body-centred cubic ferrite before melting at 1538 °C. D Quenching from high temperature into cold water is often used to harden steel. E Iron undergoes a reversible shape change under stress (shape memory effect)Explanation / Answer
23. Iron alloyed with platinum undergoes a partially reversible change under stress, but the reversibility depends upon the concentration of platinum. So option E is wrong , all other options are correct.
24. D. Covalent bonds hold the atoms in a polymer and secondary bonds hold the polymer molecules together. The synthesised polymers may have silicon or carbon backbone but the organic or natural polymers have a backbone of carbon and hydrogen.
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