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Which of the following arrangements shows schematic alignment of magnetic moments of antiferromagnetic substances?
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Which of the following statements is not true?
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A ferromagnetic substance becomes a permanent magnet when it is placed in a magnetic field becuase ______.
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The value of magnetic moment is zero in the case of antiferromagnetic substances because the domains:
(i) get oriented in the direction of the applied magnetic field.
(ii) get oriented opposite to the direction of the applied magnetic field.
(iii) are oppositely oriented with respect to each other without the application of magnetic field.
(iv) cancel out each other’s magnetic moment.
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Which of the following statements are correct?
(i) Ferrimagnetic substances lose ferrimagnetism on heating and become paramagnetic.
(ii) Ferrimagnetic substances do not lose ferrimagnetism on heating and remain ferrimagnetic.
(iii) Antiferromagnetic substances have domain structures similar to ferromagnetic substances and their magnetic moments are not cancelled by each other.
(iv) In ferromagnetic substances all the domains get oriented in the direction of magnetic field and remain as such even after removing magnetic field.
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How does a delta form at the meeting place of sea and river water?
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In solid state \[\ce{PCl5}\] is a ______.
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Reduction potentials of some ions are given below. Arrange them in decreasing order of oxidising power.
| Ion | \[\ce{CIO^{-}_{4}}\] | \[\ce{IO^{-}_{4}}\] | \[\ce{BrO^{-}_{4}}\] |
| Reduction potential EΘ/V |
EΘ = 1.19 V | EΘ = 1.65V | EΘ = 1.74 V |
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Which of the following is isoelectronic pair?
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Which of the following statements are true?
(i) Only type of interactions between particles of noble gases are due to weak dispersion forces.
(ii) Ionisation enthalpy of molecular oxygen is very close to that of xenon.
(iii) Hydrolysis of XeF6 is a redox reaction.
(iv) Xenon fluorides are not reactive.
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Give reason to explain why ClF3 exists but FCl3 does not exist.
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DNA and RNA contain four bases each. Which of the following bases is not present in RNA?
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Which one of the following would feel attraction when placed in magnetic field: Co2+, Ag+, Ti4+, Zn2+
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Given below are two statements labelled as Assertion (A) and Reason (R).
Assertion: Magnetic moment values of actinides are lesser than the theoretically predicted values.
Reason: Actinide elements are strongly paramagnetic.
Select the most appropriate answer from the options given below:
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Read the passage carefully and answer the questions that follow:
|
Strengthening the Foundation: Chargaff Formulates His "Rules" Many people believe that James Watson and Francis Crick discovered DNA in the 1950s. In reality, this is not the case. Rather, DNA was first identified in the late 1860s by Swiss chemist Friedrich Miescher. Then, in the decades following Miescher's discovery, other scientists- notably, Phoebus Levene and Erwin Chargaff- carried out a series of research efforts that revealed additional details about the DNA molecule, including its primary chemical components and the ways in which they joined with one another. Without the scientific foundation provided by these pioneers, Watson and Crick may never have reached their groundbreaking conclusion of 1953: that the DNA molecule exists in the form of a three-dimensional double helix. |
Answer the following questions:
- A segment of DNA has 100 adenine and 150 cytosine bases. What is the total number of nucleotides present in this segment of DNA?
- A sample of hair and blood was found at two sites. Scientists claim that the samples belong to same species. How did the scientists arrive at this conclusion?
- The sample of a virus was tested and it was found to contain 20% adenine, 20% thymine, 20% guanine and the rest cytosine. Is the genetic material of this virus (a) DNA-double helix (b) DNA-single helix (c) RNA? What do you infer from this data?
OR
How can Chargaff’s rule be used to infer that the genetic material of an organism is double-helix or single-helix?
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DNA fingerprinting is used to determine paternity of an individual. Which property of DNA helps in the procedure?
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In terms of band theory, what is the difference between a conductor and an insulator?
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In terms of band theory, what is the difference between a conductor and a semiconductor?
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Sea is the greatest source of some halogens. Comment.
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Give reasons for the following:
Electron gain enthalpies of halogens are largely negative.
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