Chemistry MCQs

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Caesium is the least electronegative element in the periodic table and Fluorine is the most electronegative. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.

Notes:
Fluorine is most active because it has the highest electronegativity.

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Bakelite is a thermosetting plastic formed from phenol and formaldehyde, used in electrical insulators and cookware handles. Unlike thermoplastics, it hardens irreversibly when heated and cannot be remolded. It was the first synthetic plastic, invented by Leo Baekeland in 1907.

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When iron or any other metal oxidizes, oxygen from the air combines with the iron to make iron oxide or rust. So, weight of the bar increases, due to the increased weight of oxygen which has combined with the iron. over time, the weight of the iron bar will tend to decrease, due to factors related more to erosion than to chemistry.

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Electronegativity is defined as an atom’s ability to attract an electron pair when forming a covalent bond. This property increases as you move left to right across the periodic table due to an increase in the nuclear charge’s attractive forces. It decreases as you move top to bottom, owing to the shielding effect of sub-levels and increased atomic radius, which makes electrons easier to remove. This culminates in Fluorine, being the highest and furthest to the right on the periodic table, hence it is the most electronegative.

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Noble metals, such as gold, silver, and platinum, are primarily characterized by their non-reactive nature. This means they resist oxidation and corrosion, making them ideal for use in jewelry and electronics. Unlike base metals, noble metals do not easily form compounds with other elements, which is why they maintain their luster and appearance over time. Their rarity and preciousness are secondary characteristics, but their chemical stability is what truly defines them as noble.

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Sublimation is a transition from solid to gas, bypassing the liquid phase. Iodine sublimes, producing violet vapors; naphthalene sublimes, hence its use in mothballs; and camphor also sublimes, used in medicinal and aromatic applications. Thus, all three substances exhibit sublimation upon heating, making ‘All of them’ the correct answer.

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Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpetre or saltpetre. It is also known as “Chinese snow”. Major uses of potassium nitrate are in fertilizers, rocket propellants and fireworks.

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The compound zinc oxide (ZnO) is called philosopher's wool. ZnO is a white powder that is insoluble in water. Zinc oxide is used as an additive in sun screens, sun lotions, in rubber manufacturing and in photocopying products. Alchemists, as part of their rituals, burn zinc in air and collect the residue, which formed into white woolly tufts. They called it Lana philosophica in Latin, meaning philosopher's wool.

Notes:
There are six groups of p–block elements in the periodic table numbering from 13 to 18.