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NEET Test 127

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NEET Test 127
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Weekly Quiz Competition
  • Question 1
    4 / -1

    Among the following select the alkane that is expected to have lowest boiling point:

    Solution

    The temperature at which vapor pressure of liquid becomes equal to the atmospheric pressure is called the boiling point of the liquid.

    Boiling points of hydrocarbons like alkanes are affected by several factors.

    For alkanes, the boiling point increases as molecular mass increases. This is because the intermolecular Van der Waals force increases as molecular size increases.

    Hexane, 2 -methylpentane, 3 -methylpentane, and 2,2 -dimethylbutane have the same molecular formula but different structural formula. Such compounds are called structural isomers of each other. These structures differ in the length of continuous parent carbon chains. The structures are as follows-

    For isomeric alkanes, we observe an interesting pattern in the boiling point. In case of isomeric alkanes, the boiling point decreases as branching in the molecule increases. This is because as the number of branched chains in the molecule increases it gains the shape like a sphere. Now because of the spherical shape, the molecule has less area of contact and therefore the intermolecular force between the spherical molecules becomes weak. Now, these weak intermolecular forces can be overcome at relatively low temperatures.

    In the above structures, we can see that 2,2 -dimethylbutane has the highest branching as compared to the other structures. Hence it will have the lowest boiling point.

    Hence, the correct option is (D).

     

  • Question 2
    4 / -1

    Which of the following statements is correct?

    Solution

    Chondrichthyes: These are marine animals with a streamlined body and cartilaginous endoskeletal. A placental mammal (subclass Eutheria), any member of the mammalian group, is recognized by the presence of a placenta, which facilitates the exchange of nutrients and wastes between the blood of the mother and the fetus. Invertebrates include all living mammals, except marsupials and monotremes. Cyclostomes are marine, but they migrate to fresh water for spawning. After spawning, within a few days, they die. After metamorphosis, their larvae return to the ocean. Kilons and testudos (reptiles) are not able to maintain a constant body temperature.

    Hence, the correct option is (B).

     

  • Question 3
    4 / -1

    A person can see clearly only upto a distance of 25 cm. He wants to read a book placed at a distance of 50 cm from his eyes. What is the power of the lens of his spectacles?

    Solution

    For correcting myopia, a concave lens is used and for the lens. 

     

  • Question 4
    4 / -1

    A table tennis ball that has been covered with a conducting point is suspended by a light thread so that it hangs between two metal p.a.es. One plate is earthed, while the other is attached to a high voltage generator, the ball

    Solution

    By induction, the tennis ball gets -ve charge and gets attracted to the +ve plate and touches it. Charges are then shared, as charges repel and hence ball moves away & touches the earthed plate which gives its charge and goes to initial position & process repeats.

    Hence, the correct option is (B).

     

     

  • Question 5
    4 / -1

    In a solid 'AB' having the NaCl structure, 'A' atoms occupy the corners of the cubic unit cell. If all the face centred atoms along one of the axes are removed, then the resultant stoichiometry of the solid is:

    Solution

    Na in NaCl has eight corner and six face atoms and thus, if we remove face centred atom of one axis, then two face atoms are removed. Thus, A is at 8 corners & at 4 face centers. 

    Number of A atoms per unit cell 

    = 8 × 1/8 + 4 × 1/2 = 3

    B present in all octahedral voids, hence Number of B atoms per unit cell =12 × 1/4 + 1 = 4

    Thus, formula is A3 B4.

    Hence, the correct option is (D).

     

     

  • Question 6
    4 / -1

    Which of the following is the most dangerous metal pollutant of automobile exhaust?

    Solution

    Automobiles burn petroleum inefficiently causing 80% of air pollution and 75% of noise pollution in urban areas. They release hydrocarbons (13.7%), carbon monoxide (77.2%), nitrogen oxides (7.7%), sulphur oxides, ammonia, aldehydes and lead (90% of total lead poisoning). Lead is present in petroleum in the form of Pb(CH3)4 and Pb(C2H5)4 as antiknock agent.

    Hence, the correct option is (D).

     

  • Question 7
    4 / -1

    Which of the following is a wrong statement about myelin sheath?

    Solution

    Neurilemma (also known as neurolemma, sheath of Schwann, or Schwann's sheath) is the outermost nucleated cytoplasmic layer of Schwann cells (also called neurilemmocytes) that surrounds the axon of the neuron.In the central nervous system, axons are myelinated by oligodendrocytes, thus lack neurilemma.

    Schwann cells make myelin in the peripheral nervous system (PNS: nerves) and oligodendrocytes in the central nervous system (CNS: brain and spinal cord). In the PNS, one Schwann cell forms a single myelin sheath.

    Hence, the correct option is (D).

     

     

  • Question 8
    4 / -1

    When m-chlorobenzaldehyde is treated with 50% KOH solution, the product(s) obtained is/are:

    Solution

    When m-chlorobenzaldehyde is treated with 50% KOH solution, the product(s) obtained is (are) potassium meta chloro benzoate and meta chloro benzyl alcohol. 

    In this reaction, there is no alpha hydrogen atom present in meta chloro benzaldehyde. 

    So, it undergoes a Cannizzaro reaction in which one molecule is oxidized to meta chloro benzoic acid and another molecule is reduced to meta chloro benzyl alcohol.

    Hence, the correct option is (C)

     

  • Question 9
    4 / -1

    At a particular locus, the frequency of ′A′ allele is 0.6 and that of ′a′ is 0.4. What would be the frequency of heterozygotes in a randomly mating population of equilibrium?

    Solution

     

  • Question 10
    4 / -1

    Which of the following multicellular animals does not have nerve cells or neurons to respond to stimuli?

    a. Anemone

    b. Sponge

    c. Hydra

    Solution

    Sponges have no nervous system or organs like most animals do. While adult sponges are not mobile, they are able to react to certain physical stimuli despite lacking conventional organs and sensory systems. Sponges have no nerves or brain, so they lack any ability to cognitively control their movement.

    Hence, the correct option is (B).

     

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