JEE Advanced 2020 · Paper 2 · Chemistry Q7

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ChemistryMultiple correct+4 / -2Question 25 of 54

In an experiment, $m$ grams of a compound X (gas/liquid/solid) taken in a container is loaded in a balance as shown in figure I below. In the presence of a magnetic field, the pan with X is either deflected upwards (figure II), or deflected downwards (figure III), depending on the compound X. Identify the correct statement(s).

Three panels of a beam balance with mass m on one pan and compound X on the other. (I) Balanced, no magnetic field. (II) With X between the poles (N, S) of a magnet, the X pan is pushed upward. (III) With the field present the X pan is pulled downward.

If X is

\ce{H2O}(l)

, deflection of the pan is upwards.

If X is

\ce{K4[Fe(CN)6]}(s)

, deflection of the pan is upwards.

If X is

\ce{O2}(g)

, deflection of the pan is downwards.

If X is

\ce{C6H6}(l)

, deflection of the pan is downwards.

Answer and worked solution

Official answer: A, B, C

In a non-uniform field a paramagnetic sample is pulled into the field, so its pan goes down. A diamagnetic sample is pushed out of the field, so its pan goes up.

(A) $\ce{H2O}$ is diamagnetic: upwards. True.
(B) $\ce{K4[Fe(CN)6]}$ contains low-spin $\ce{Fe^{2+}}$ ( $t_{2g}^6$ , no unpaired electrons). It is diamagnetic: upwards. True.
(C) $\ce{O2}$ has two unpaired electrons in its π* orbitals, so it is paramagnetic: downwards. True.
(D) Benzene is diamagnetic, so it would move upwards. False.

(A), (B), (C)

Topics:Magnetic properties and colour Molecular orbital theory

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JEE Advanced 2020 · Paper 2, Chemistry question 7