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FBISE Chem-Supp(2019 ) MCQs and Answers with explanation

FBISE Chem-Supp(2019 ) MCQs and Answers with explanation

1. Metal carbonates decompose on heating to give metal oxides and carbon dioxide. Which of the following metal carbonates is most thermaly stable?





... Answer is d)
Explanation:Thermal stability of carbonates of alkaline earth metal increases down the group. This is because of the fact that charge density of metal ions decreases due to increase in atomic size from top to bottom in the group. Metal ion with high charge density causes distortion of carbonate ions and results in formation of CO2 easily as compared to metal ions with lower charge density. Therefore, a metal ion with lower charge density has lesser chances of breaking down the carbonate and requires high energy.

2. For a mixture containing 50% (+)tartaric acid and 50% (-)tartaric acid, which of following statements is correct?





... Answer is b)
Explanation: (+) tartaric acid is dextro rotatory as it rotates plane polarized light in clockwise direction and (-) tartaric acid is levorotatory as it rotates plane polarized light in anti-clockwise direction. A racimic mixture contains 50% (+) and 50% (-) forms is optically inactive.

3. Which of the following occurs during the initiation stage of radical mechanism?





... Answer is c)
Explanation: Thermal condition or uv light causer neutral molecule to undergo homolytic cleavage of a sigma bond to produce a diradical.

4. Which of the following will give benzoic acid, when reacted with alkaline KMnO4?





... Answer is c)
Explanation:Benzoic acid is formed form oxidation of side chain attached with benzene ring in toluene with alkaline KMnO4.

5. Which of the following is not monohydric alcohol?





... Answer is c)
Explanation: Monohydric alcohols are alcohols that contain only one -OH group. Glycole is a dihydric alcohol as it contains two -OH groups attached to two carbon atoms.

6. Identify the X in the following reaction:





... Answer is a)
Explanation: Iodofom test is given by those aldehydes or ketones which contain acetyl (CH3CO) group. Among these compounds only acetaldehyde and acetone give idoform test. However, acetaldehyde can give sodium formate while aceton can give sodium acetate in addtion to idoform (CHX3) product. In chemical equation, formation of Sodium formate indicate that X is acetalehyde.

7. The order of reactivity of alcohol with respect to -O-H bond cleavage is

    <



... Answer is a)
Explanation: If an electrophile attacks on the O-H bond, the order of reactivity of alcohols is as follow:CH3OH> 1 Alcohol> 2 Alcohol> 3 Alcohol. Reason is that when an electrophile attacks hydrogen of O-H group, an alkoxide (RO-)is formed. Eease of this reaction depends upon the stability of alkoxide ion. As methyloxide is the most stable, so it is easily formed and hence most reactive. On the other hand, tertiary alkoxide is least stable due electon donating effect of three methyl groups, so it is not esily formed and hence least reactive.

8. Indicate the most acidic carboxylic acid





... Answer is d)
Explanation: Acidic strength of an acid depends upon the stability of its carboxylate ions (conjugate base). Greater the stability of carboxylate ions, stronger will be an acid and vice versa. Among these acids, dichlorethanoic acid is the strongest acid as its conjugate base is the most stable due to strong electron withdrawing effect of two chloro groups,

9. Hydrolysis of triglycerides by alkalis is called





... Answer is a)
Explanation: Hydrolysis of triglycerides by alkalie produces soap, so it is called saponification.

10. Which of following compound is not used to adhere two items together?





... Answerq10 d)
Explanation: Dye is not used to adhere the two items togehter. .

11. Designing and creation of chemicals that are not hazardous to people or environment is related to





... Answer is b)
Explanation:By definition, green chemistry is the branch of chemistry that deals with designing and creation of chemicals that are not hazardous to people or environment.

12. Very high energy beam of electron is used in





... Answer is c)
Explanation: All spectroscopic techniques involves the interaction of electromagnetic raditions with matter while in mess spectrometry, very high energy beam of electron is use to prouduce molecular and fragment ions.

13. Good leaving group among the following is





... Answer is b)
Explanation: All weak bases and neutral molecules are good leaving grousps. From above species, H2O is the weaker base and neutral molecule, so it is good leaving group.

14. Which of the following is not a hydrocarbons?





... Answer is b)
Explanation: The organic compounds which contain carbon and hdrogen are called hydrocarbons. Resorcinol is not a hydrocarbon as it contains OH groups. .

15. Which of the following is an amphoteric hydroxide?





... Answer is a)
Explanation: The hydroxides that show the properties of acid and base are known as amphoteric hyroxides.

16. Coordination number of carbonyl in [Ni(CO)4] is





... Answer is a)
Explanation: Coordination number is the number of electrons pair donated by ligand to central metal atom or ions. In this example, there are four electron pairs that are donated by CO groups to Ni atom.

17. 1,3-Dibromobutane is





... Answer is a)
Explanation: 1,3-Dibromobutane is a dihalide. For vicinal dihalides, two halogens are attached to adjacent carbon atoms. For geminal dihalides, two halogens are attached to same carbon atom.

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