Chemistry

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Showing 276 to 300 of 1398 questions (page 12 of 56).

276. In a multistep reaction, the overall rate is governed by the

A. fastest step B. slowest step C. first step always D. last step always E. step with the most reactants

277. A rise in temperature of about 10 K commonly

A. halves the reaction rate B. roughly doubles the reaction rate C. has no effect on the rate D. changes the order of the reaction E. lowers the activation energy

278. The decomposition of hydrogen peroxide by manganese dioxide is an example of

A. homogeneous catalysis B. heterogeneous catalysis C. autocatalysis D. enzyme catalysis E. negative catalysis

279. A substance that decreases the rate of a reaction is called

A. a promoter B. an inhibitor C. a catalyst poison for enzymes only D. an activator E. a co-factor

280. The element with the highest electronegativity is

A. oxygen B. chlorine C. fluorine D. nitrogen E. caesium

281. Metallic character generally

A. increases across a period B. decreases down a group C. increases down a group D. is unrelated to position E. is highest for noble gases

282. The screening or shielding effect of inner electrons

A. increases the effective nuclear charge B. decreases the effective nuclear charge felt by outer electrons C. has no effect on atomic size D. increases ionization energy E. only applies to d electrons

283. The number of elements in the fourth period of the periodic table is

A. 2 B. 8 C. 18 D. 32 E. 10

284. Alkali metals are stored under kerosene oil because they

A. are volatile B. react vigorously with air and moisture C. dissolve in water slowly D. are radioactive E. sublime readily

285. Among the alkali metals, lithium has the highest

A. atomic radius B. ionization energy C. density D. reactivity with water E. atomic number

286. The chemical formula of gypsum is

A. CaSO4 B. CaSO4.(1/2)H2O C. CaSO4.2H2O D. CaCO3 E. CaO

287. Sodium carbonate is used industrially mainly in the manufacture of

A. glass B. fertilizer C. plastics D. petrol E. cement

288. Carbon monoxide is highly toxic because it

A. is acidic B. binds strongly to haemoglobin in place of oxygen C. dissolves in water D. decomposes in the lungs E. reacts with nitrogen

289. The catalyst used in the contact process for manufacturing sulphuric acid is

A. iron B. vanadium pentoxide C. platinum D. nickel E. aluminium chloride

290. Silicon carbide is used as an abrasive because it is

A. highly ionic B. a covalent network solid of great hardness C. a soft molecular solid D. metallic E. volatile

291. Concentrated nitric acid acts on copper mainly as

A. a reducing agent B. an oxidizing agent C. a dehydrating agent D. a catalyst E. a base

292. The bleaching action of chlorine water is due to

A. hydrochloric acid B. nascent oxygen from hypochlorous acid C. chlorine gas dissolving the dye D. reduction of the dye E. hydrogen gas

293. The oxidation state of chromium in the dichromate ion is

A. +3 B. +4 C. +6 D. +7 E. +2

294. Paramagnetism in transition metal compounds is due to

A. paired electrons B. unpaired d electrons C. the nucleus D. lattice vibrations E. delocalized pi bonds

295. Stainless steel is an alloy of iron with

A. copper and tin B. chromium and nickel C. lead and zinc D. aluminium and silicon E. carbon only

296. In acidic medium, permanganate ion is reduced to

A. MnO2 B. Mn2+ C. MnO4 2- D. Mn metal E. Mn3+

297. Successive members of a homologous series differ by

A. CH3 B. CH2 C. C2H4 D. H2 E. CH4

298. The number of structural isomers of butane, C4H10, is

A. 1 B. 2 C. 3 D. 4 E. 5

299. The Wurtz reaction is used to prepare

A. alkenes from alcohols B. symmetrical alkanes from alkyl halides C. alkynes from dihalides D. alcohols from esters E. ketones from acids

300. Dehydration of ethanol with concentrated sulphuric acid gives

A. ethane B. ethene C. ethyne D. ethanal E. ethanoic acid

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