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The number of bicarbonates that do not exist in solid form among the following is....................
    Correct answer is '4'. Can you explain this answer?

    Krishna Iyer answered
    No bicarbonates exist in solid due to inefficient packing except Ammonium and Na+ to Cs+. Only NaHCO3 , KHCO3 , RbHCO3 , CsHCO3 and NH4HCO3 exist in solid.
    So the correct answer is 4.

    Can you explain the answer of this question below:
    On the basis of aromaticity, there are three types of compounds i.e. aromatic, non-aromatic and antiaromatic.
    The increasing order of stability of these compounds are is under:
    Anti-aromatic compound < non-aromatic compound < aromatic compounds. Compounds to be aromatic
    follow the following conditions (according to valence bond theory)
    (i) The compounds must be be cyclic in structure having (4n + 2)π e–, where n = Hückel’s number = 0, 1,
    2, 3 et.c
    (ii) The each atoms of the cyclic structure must have unhybridised p-orbital i.e. the atoms of the
    compounds have unhybridised p-orbital i.e. usually have sp2 hybrid or planar.
    (iii) There must be a ring current of π electrons in the ring or cyclic structure i.e. cyclic structure must
    undergo resonance .
    Compounds to be anti-aromatic, it must have 4nπe– where n = 1, 2… and it must be planar and undergo
    resonance. Non-aromatic compounds the name itself spells that compounds must be non-planar
    irrespective of number of π electrons. Either it has 4nπe– or (4n + 2) π electrons it does not matter.
    The rate of reaction of any aromatic compounds depends upon the following factors:
    (i) Electron density
    (ii) stability of carbocation produced
    Higher the amount of electron density of the ring, higher will be its rate towards aromatic electrophilic
    substitution and vice-versa. Similarly, higher will be the stability of the produced carbocation after the
    attack of electrophile, higher will be its rate towards aromatic electrophilic substitution. There is a great
    effect of kinetic labelling on the rate of aromatic electrophilic substitution. As we known that higher the
    atomic weight or, molecualr weight, higher will be the van der Waal’s force of attraction or, bond energy.
    Since there will be effect of kienetic labelling if the 2nd step of the reaction will be the slow step, (r.d.s.)
    otherwise there will be no effect of kinetic labelling.
    Q. Which of the following is correct order of the rate of reaction of C6H6, C6D6 and C6T6 towards
    nitrations?
    • A:
      C6H6 >C6D6 > C6T6
    • B:
      C6H6 = C6D6 = C6T6
    • C:
      C6H6 > C6D6 = C6T6
    • D:
      C6T6 >C6D6 >C6H6
    The answer is b.

    Pranavi Chavan answered
    B
    2nd step is fast step in nitration.

    Valence shell electron-pair repulsion theory predicts the shape of a molecule by considering the most stable configuration of the bond angles in the molecule. The main points of the theory are
    (i) Electron pairs in the valence shell of central atom of a molecule, whether bonding or lone pairs are regarded as occupying localised orbitals. These orbitals arrange themselves so as to minimize the mutual electronic repulsions.
    (ii) The magnitude of the different types of electronic repulsions follow the order given below:
    Lone pair-lone pair> lone pair-bonding pair > bonding pair-bonding pair. These repulsive forces alter the bond angles of the molecule or ion.
    (iii) The electron repulsion between two pairs of electrons will be minimum if they stay as far as possible. On this basis, several studied. have been done
    Which of the following statements is correct ?
    • a)
      The bond angle of NCl3 is greater than NH3 as Pπ − dπ back-bonding is present in NCl3.
    • b)
      BF3 is more acidic than BCl3 due to presence of Pπ − dπ back bonding in BF3
    • c)
      When the bond multiplicity is increased, bond angle is decreased.
    • d)
      The bond angle of SiCl4 is greater than CCl4
    Correct answer is option 'A'. Can you explain this answer?

    Lakshmi Sharma answered
    Explanation:

    NCl3 vs NH3 bond angle:
    - In NCl3, the central nitrogen atom has a lone pair of electrons and three bond pairs. Due to the presence of the lone pair, there is greater repulsion among the electron pairs, leading to a smaller bond angle compared to NH3.
    - In NH3, nitrogen has a lone pair and three bond pairs, resulting in a larger bond angle compared to NCl3.

    Therefore, the statement "The bond angle of NCl3 is greater than NH3 as Pπ − dπ back-bonding is present in NCl3" is correct.

    BF3 vs BCl3 acidity:
    - BF3 is not acidic as it does not have any H+ ions to donate, whereas BCl3 can act as a Lewis acid by accepting a lone pair of electrons.
    - The presence of Pπ − dπ back-bonding in BF3 does not make it more acidic compared to BCl3.

    Therefore, the statement "BF3 is more acidic than BCl3 due to the presence of Pπ − dπ back-bonding in BF3" is incorrect.

    Bond multiplicity and bond angle:
    - When the bond multiplicity is increased, the bond angle is not necessarily decreased. The bond angle depends on the repulsion between electron pairs and the geometry of the molecule.

    SiCl4 vs CCl4 bond angle:
    - In SiCl4 and CCl4, both central atoms have four bond pairs and no lone pairs. Since both molecules have the same geometry (tetrahedral), the bond angle in SiCl4 is greater than that in CCl4 due to the larger size of the silicon atom compared to carbon.

    Therefore, the statement "The bond angle of SiCl4 is greater than CCl4" is correct.

    If a bag contains five balls. Two balls are drawn and are found to be white. What is the probabilitythat all the balls are white?
    • a)
      1/4
    • b)
      1/3
    • c)
      1/2
    • d)
      2/3
    Correct answer is option 'C'. Can you explain this answer?

    Anjali Sharma answered
    We don't know the number of white and black balls in the bag, but we know the number of white balls can't be less than 2.

    Now, there are different cases, which are the number of white balls in the bag. The total cases are : 2c2+3c2+4c2+5c2 =20

    The question is asking to find the probability of the case that there are 5 white balls, which 5c2 = 10 cases

    So, probability =10/20=1/2

    Can you explain the answer of this question below:
    In the circuit shown C1 = 2C2. Switch S is closed at time t = 0. Let i1 & i2 be the current flowing through C1 and C2 at any time t, then the ratio I1/I2
    • A:
      is constant
    • B:
      increases with increase in time t
    • C:
      decreases with increase in time t
    • D:
      first increases then decreases
    The answer is b.

    Naina Bansal answered
    The answer is a.
    The voltage across both C1 and C2 will be same as they are parallel to each other.
    For capacitor Q= CV, this means that the capacitor C1 will have greater charge as its capacitance is more.
    But as the voltage is same the ratio of current i1/i2 will remain unchanged.
     

    Select from following molecules or ions, which is/are aromatic.
    • a)
    • b)
    • c)
    • d)
    Correct answer is option 'A,C,D'. Can you explain this answer?

    Vijay Kumar answered
    For aromatic compounds
    For a compound to be aromatic, it should follow Huckle's (4n + 2)πe− rule, i.e., 2, 6, 10, 14....πe−
    They should show delocalised, conjugate π system with alternate single and double bonds. In addition to this, the compound should be cyclic and planar or almost planar.
    The number of πe− is even, but not a multiple of 4.
    For anti-aromatic compounds:
    4nπe−, i.e., 4, 8, 12....πe− should be delocalized in a cyclic, planar, or almost planar system with alternate single and double bonds.
    Planar conjugated carbocyclic polyene, carbocyclic polyene structure is less stable than its open structure.

    If f is a periodic function and g is a non–periodic function, then which of the following is not always a non–periodic function?  
    • a)
      fog  
    • b)
      gof  
    • c)
      fof  
    • d)
      gog 
    Correct answer is option 'A,B,C'. Can you explain this answer?

    Mahi Sengupta answered
    Suppose period of f is T. Now fog may or may not be periodics. For example if f(x) = sin x and
    g(x) = x + sin x, then fog is periodic of period 2π. On the other hand if f(x) = sin x and
    g(x) = x2, then fog is a non–periodic function.
    gof is always periodic of periodic T. Similarly fof is always periodic of period T. 

    An X-ray tube produces a continuous spectrum of radiation with its short wavelength end at 0.45 Å. If the order of accelerating voltage (for electrons) is required in such a tube is (10x) kV. Then the value of x(integer) is .......
      Correct answer is '3'. Can you explain this answer?

      Ankita Kaur answered
      Given:
      - The short wavelength end of the continuous spectrum of radiation produced by an X-ray tube is 0.45 Å.
      - The order of accelerating voltage required in the tube is (10x) kV.

      To find:
      The value of x (integer).

      Solution:
      The continuous spectrum of radiation produced by an X-ray tube is due to the deceleration of high-speed electrons when they strike a metal target. The radiation emitted in this process is called bremsstrahlung radiation.

      1. Relationship between wavelength and accelerating voltage:
      The wavelength of the X-rays produced by an X-ray tube is inversely proportional to the accelerating voltage. Mathematically, this relationship can be represented as:

      λ ∝ 1/V

      Where:
      - λ is the wavelength of the X-rays
      - V is the accelerating voltage

      2. Determining the relationship between wavelength and accelerating voltage:
      We are given that the short wavelength end of the continuous spectrum is 0.45 Å. Let's denote this wavelength as λ₀.

      Using the relationship mentioned above, we can write:

      λ₀ ∝ 1/V

      3. Converting wavelength to meters:
      Since the given wavelength is in angstroms (Å), we need to convert it to meters to match the SI unit.

      1 Å = 1 × 10^(-10) m

      So, the short wavelength end (λ₀) can be written as:

      λ₀ = 0.45 × 10^(-10) m

      4. Solving for the accelerating voltage:
      Substituting the value of λ₀ into the relationship between wavelength and accelerating voltage, we have:

      0.45 × 10^(-10) m ∝ 1/V

      Simplifying, we get:

      V ∝ 1/(0.45 × 10^(-10) m)

      5. Finding the value of x:
      We are given that the order of accelerating voltage required is (10x) kV. Let's denote this value as V₀.

      V₀ ∝ 1/(0.45 × 10^(-10) m)

      To find x, we need to determine the exponent of 10 in V₀.

      Writing V₀ in scientific notation, we have:

      V₀ = 10^x kV

      Substituting this into the equation above, we get:

      10^x kV ∝ 1/(0.45 × 10^(-10) m)

      Simplifying, we have:

      10^x ∝ 1/(0.45 × 10^(-10) m)

      Taking the logarithm of both sides, we get:

      x log(10) ∝ log(1/(0.45 × 10^(-10) m))

      Since log(10) = 1, we can simplify further:

      x ∝ log(1/(0.45 × 10^(-10) m))

      x ∝ log(1) - log(0.45 × 10^(-10) m)

      x ∝ 0 - log(0.45 × 10^(-10) m)

      x ∝ -log(0.45) - log(10^(-10) m)

      Using logarithmic properties, we have:

      x ∝ -log

      A number is selected at random from the set of natural numbers. The probability that the sum of the digits of its square is 39 is
      • a)
        1/6
      • b)
        0
      • c)
        1/10
      • d)
        1/9
      Correct answer is option 'B'. Can you explain this answer?

      Sanaya Patel answered
      Explanation:

      Let's assume the number selected is n.

      Step 1: Finding the range of n

      We know that the sum of the digits of n^2 cannot be greater than the sum of the digits of n*9, i.e., 81. So, the maximum value of n can be found as follows:

      n*9 < 10^k="" (where="" k="" is="" the="" number="" of="" digits="" in="" />
      9n < />
      n < />

      Therefore, the maximum value of n is 111, since 10^3/9 = 111.11.

      Step 2: Finding the probability

      We need to find the probability that the sum of the digits of n^2 is 39. Let's assume that the sum of the digits of n is x. Then, the sum of the digits of n^2 can be written as:

      (x^2 - 2s) (where s is the sum of the digits of x^2)

      We know that x can range from 1 to 19 (since the maximum value of n is 111). So, we can calculate the value of s for each value of x and find the number of values of s that give a sum of 39.

      After calculating, we get that there are no values of s that give a sum of 39. Therefore, the probability is 0.

      Hence, the correct answer is option 'B'.

      Find the point p on the line 2x + 3y + = 0 such that |PA - PB| is maximum where A is (2,0) and B is (0,2)
      • a)
        (1, –1)
      • b)
        (7, –5)
      • c)
        (–2, 1)
      • d)
        (4, –3)
      Correct answer is option 'B'. Can you explain this answer?

      Naina Kumar answered
      Thus the max value of |PA – PB| is AB
      This is possible only when P lies on AB but P lies on AB
      ∴ P is the point of intersection of x + y = 2 and 2x + 3y + 1 = 0.

      Let Z1 and Z2 complex numbers such that Z1 ≠ Z2 and |Z1| = |Z2|. If Z1 has positive real part and Z2 has negative imaginary part, then may be
      • a)
        zero
      • b)
        real and positive
      • c)
        real and negative
      • d)
        purely imaginary
      Correct answer is option 'A,D'. Can you explain this answer?

      Vijay Kumar answered
      Given Z1 ≠ Z2 and |Z1| and |Z2|
      Z1 has positive real part and
      Z2 has negative imaginary part
      Then there can be following cases
      When a, b are positive real numbers
      Also,
      When a, b are non negative real numbers
      Similarly in all the other cases
      is always purely imaginary
      is either zero or purely imaginary.

      Consider a titration of potassium dichromate solution with acidified Mohr's salt solution using diphenylamine as indicator. The number of moles of Mohr's salt required per mole of dichromate is
        Correct answer is '6'. Can you explain this answer?

        Rhea Datta answered
        The titration of potassium dichromate (K2Cr2O7) with acidified Mohr's salt solution involves the oxidation-reduction reaction between dichromate ions (Cr2O7^2-) and Mohr's salt ions (Fe^2+).

        Reaction:
        Cr2O7^2- + 6Fe^2+ + 14H+ -> 2Cr^3+ + 6Fe^3+ + 7H2O

        Explanation:
        1. The potassium dichromate solution is acidified to provide an acidic medium for the reaction to occur.
        2. Mohr's salt solution is prepared by dissolving ammonium iron(II) sulfate hexahydrate [(NH4)2Fe(SO4)2 · 6H2O] in distilled water.
        3. Diphenylamine is used as an indicator in this titration. It is colorless in the presence of dichromate ions and turns blue in the presence of excess Fe^2+ ions.
        4. Initially, the potassium dichromate solution is added to the Mohr's salt solution drop by drop until the blue coloration appears, indicating the presence of excess Fe^2+ ions.
        5. At this point, the reaction between dichromate ions and Fe^2+ ions is complete, and the number of moles of Mohr's salt required per mole of dichromate can be determined.

        Calculation:
        The balanced equation shows that 6 moles of Fe^2+ ions are required to react with each mole of dichromate ions. Therefore, the number of moles of Mohr's salt required per mole of dichromate is 6.

        Conclusion:
        In this titration, 6 moles of Mohr's salt are needed to react completely with 1 mole of potassium dichromate.

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