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Chemistry NEET Questions — Free MCQ Practice

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$I P_{1}$ and $I P_{2}$ Mg are 178 and 348 Kcal $m o l^{- 1}$ . The energy required for the reaction,

Mg $\to$ $M g^{2 +} + 2 e^{-}$ is :

A.

+170 Kacl

B.

+526Kacl

C.

-170Kacl

D.

-526Kacl

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Explanation

(b) Removal of two electrons (one by one ) from an atom requries energy = $I P_{1}$ + $I P_{2}$ .

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Which of the following characteristics regarding halogens is not correct?

A.

Ionization energy decreases with increases in atomic number

B.

Electronegativity decreases with increases in atomic number

C.

Electron affinity decreases with increases in atomic number

D.

Enthalpy of fusion increases with increases in atomic number

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Explanation

(c) Electron affinity order for halogen is $C l > F > B r > I$ .

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The process requiring the absorption of energy is :

A.

$F \to F^{-}$

B.

$H \to H^{-}$

C.

$C l \to C l^{-}$

D.

$O \to O^{2 -}$

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Explanation

(d) $E A_{1}$ for elements is exothermic and $E A_{2}$ is endothermic. Also $E A_{2}$ for $O > E A_{1}$ for O.

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Which of the following orders is correct for the size?

A.

$M g^{2 +} < N a^{+} < F^{-} A l$

B.

$A l^{3 +} < M g^{2 +} L i^{+} < K^{+}$

C.

$F e^{4 +} < F e^{3 +} < F e^{2 +} < F e$

D.

$M g > A l > S i > P$

(A) (1), (2) & (3) (B) (2), (3) & (4)

(C) (1), (3) & (5) (D) (1), (2), (3) & (4)

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Explanation

(D) (1) $M g^{2 +}, N a^{+} a n d F^{-}$ are isoelectronic and thus follows the order ${}_{12}M g^{2 +} < {}_{11}N a^{+} < {}_{9}F_{-}$ .

Al belongs to third period and has no charge so it is largest.

$N a^{+} = 102 p m; M g^{2 +} = 72 p m; A l = 143 p m, F^{-} = 133 p m .$

$K^{+}$ = has more number of shells than $M g^{2 +} a n d A l^{3 +} a n d M g^{2 +}$ are isoelectronic but $A l^{3 +}$ has higher nuclear charge so $A l^{3 +} < M g^{2 +} . M g^{2 +} a n d L i^{+}$ has diagonal relationship. But due to +2 charge in $M g^{2 +}, t h e M g^{2 +}$ is smaller than $L i^{+}$ . Hence $A l^{3 +}$ is the smallest one.

$K^{+} = 1.38 A, L i^{2 +} = 0.76 A, M g^{2 +} = 0.72 A a n d A l^{3 +} = 0.535 A .$

As the number of electrons are lost, the attraction between valence shell electrons and nucleus increases. As a consequence of this the electrons are pulled closer to the nucleus leading to the contraction in size of ions.

Across the period the nuclear charge increases and thus the size of atoms decreases.

Mg = 160 pm; Al = 143 pm; Si = 118; P = 110 pm.

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The electron gain enthalpies of halogens in kJ mol-1 are as given below.

F =-332, Cl =-349, Br =-234, I =-295.

The least negative value for F as compared to that of Cl is due to:

A.

Strong electron-electron repulsions in the compact 2p-subshell of F.

B.

Weak electron-electron repulsions in the bigger 3p-subshell of Cl.

C.

Smaller electronegativity value of F than Cl.

D.

(A) & (B) both

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Explanation

(D) Due to small size of F atom, the electron-electron repulsions in compact 2-p sub shell are large and hence the incoming electron is not accepted with the same ease as is the case with Cl (less electron - electron repulsions)

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Which of the following statements is not correct?

A.

The first ionization energies (in KJ $m o l^{- 1}$ ) of carbon, silicon, germanium, tin, and lead are 1086, 786, 761, 708 and 715 respectively.

B.

Down the group, electronegativity decreases from B to Tl in boron family.

C.

Among oxides of the elements of carbon family, CO is neutral, GeO is acidic and SnO is amphoteric.

D.

The 4f- and 5f- inner transition elements are placed separately at the bottom of the periodic table to maintain its structure.

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Explanation

(A), (C) and (D) are correct statements

(B) First decreases from B to Al and then increases marginally owing to discrepancies in atomic size of the element.

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Which of the following orders is correct?

A.

F>N>C>Si>Ga -non-metallic character.

B.

F>Cl>O>N - oxidising property.

C.

C<Si>P>N - electron affinity value.

D.

All of these.

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Explanation

(D) (A) As electronegativity increases the non-metallic character increases as tendency to form anion increases.

(B) It is based on their SRP values. (Oxidising power may be cumulative effect of hydration energies, electronegativities, bond dissociation energies and electron gain enthalpies)

(C) C =-121; Si = -135; P =-60; N = +31 (all values are in KJ/mole). It depends on various factors like size of atom, nuclear charge, partially filled, half filled and completely filled electronic configurations.

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If the same element is forming oxides in different oxidation states then :

A.

that oxides will be neutral in nature in which element will be in its highest oxidation state.

B.

that oxide will be highest acidic in nature in which element will be in this highest oxidation state.

C.

that oxide will be amphoteric in nature in which element will be in its highest oxidation state.

D.

that oxide will be highly basic in nature in which element will be in its highest oxidation state.

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Explanation

(B) Oxidation state $\propto$ electronegativity.

Electronegativity increases with increase in oxidation state; so the difference in electronegativity decreases (between element and oxygen) and acidic character increases.

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Assertion : The $5^{t h}$ period of periodic table contains 18 elements and not 32.

Reason : n = 5, –1 = 0, 1, 2, 3. The order in which the energy of available orbits 4d, 5s and 5p increases is 5s < 4d < 5p and the total number of orbitals available are 9 and thus 18 electrons can be accommodated.

A. If both the assertion and the reason are true and the reason is a correct explanation of the assertion B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion C. If the assertion is true but the reason is false D. If both the assertion and reason are false

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Explanation

The order in which the energy of available orbitals `4d,5s` and 5p increases is `5s lt 4d lt 5p` and the total number of orbitals avaiable are 9 and thus 18 electrons can be accommodated

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Assertion : :The 4f- and 5f- inner transition series of elements are placed separately at
the bottom of the periodic table.

Reason : (i) This prevents the undue expansion of the periodic table i.e., maintains its structure.
(ii) This preserve the principle of classification by keeping elements with similar properties in a single column.

A. If both the assertion and the reason are true and the reason is a correct explanation of the assertion B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion C. If the assertion is true but the reason is false D. If both the assertion and reason are false

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Explanation

(A)

4f and 5f - inner transition series of elements are placed separately at the bottom of the periodic table. It is because

1) It prevents the undue expansion of the periodic table i.e. maintains it's structure.

2) This preserves the principle of classification by keeping elements with similar properties in a single column.

Chemistry MCQs for NEET — Practice Questions with Answers

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