d and f Block Elements — Page 9 | NEET Chemistry

Q81

The transition metal ions responsible for color in ruby and emerald are, respectively :

A Cr3+ and Co3+

B Co3+ and Cr3+

C Co3+ and Co3+

D Cr3+ and Cr3+

Correct Answer

Option D

Solution

On addition of impurities to the colourless gemstones, brilliant colours are produced.

On addition of chromium to colourless corundum (Al2O3), a red ruby is formed.

Red colour ruby is obtained when Cr3+ ions replace Al3+ ions in the octahedral sites of corundum.

A green emerald emerges when chromium is added to colourless beryl (Be3Al2(SiO3)6).

Green colour emerald is obtained when Cr3+ ions replace Al3+ in the octahedral site of beryl.

Q82

The transition element that has lowest enthalpy of atomisation, is :

A Fe

B Cu

C V

D Zn

Correct Answer

Option B

Solution

Since Zn is not a transition element so transition element having lowest atomisation energy out of Cu, V, Fe is Cu.

Q83

Sulphide ion is soft base and its ores are common for metals. (a) Pb (b) Al (c) Ag (d) Mg

A (a) and (c) only

B (a) and (d) only

C (a) and (b) only

D (c) and (d) only

Correct Answer

Option A

Solution

Pb and Ag commonly exist in the form of sulphide ore like Pbs (galena) and Ag2S (Argentite) 'Al' is mainly found in the form of oxide ore whereas 'Mg' is found in the form of halide ore.

Q84

Which one of the following reactions does not occur during extraction of copper?

A

\mathrm{2FeS + 3{O_2} \to 2FeO + 2S{O_2}}

B

\mathrm{FeO + Si{O_2} \to FeSi{O_3}}

C

\mathrm{CaO + Si{O_2} \to CaSi{O_3}}

D

\mathrm{2C{u_2}s + 3{O_2} \to 2C{u_2}O + 2S{O_2}}

Correct Answer

Option C

Solution

\begin{aligned} & \mathrm{CuFeS}_2+\mathrm{O}_2 \stackrel{\text{ Partial roasting }}{\longrightarrow} \\\\ & \mathrm{Cu}_2 \mathrm{~S}+\mathrm{FeO}+\mathrm{SO}_2+\underset{\text{ very small }}{\mathrm{FeS}}+\underset{\text{ very small }}{\mathrm{Cu}_2 \mathrm{O}} \\\\ & \mathrm{Cu}_2 \mathrm{~S}+\mathrm{O}_2 \rightarrow \mathrm{Cu}_2 \mathrm{O}+\mathrm{SO}_2 \\\\ & \mathrm{FeS}+\mathrm{O}_2 \rightarrow \mathrm{FeO}+\mathrm{SO}_2 \\\\ & \mathrm{FeO}+\mathrm{SiO}_2 \rightarrow \mathrm{FeSiO}_3 \end{aligned}

No formation of calcium silicate $\left(\mathrm{CaSiO}_3\right)$ in extraction of $\mathrm{Cu}$ .

Q85

The pair that does NOT require calcination is -

A Fe2O3 and CaCO3⋅MgCO3

B ZnCO3 and CaO

C ZnO and Fe2O3⋅xH2O

D ZnO and MgO

Correct Answer

Option D

Solution

In calcination, we convert a compound or ore into oxide.

In option (D) you can see there is ZnO and MgO, as they are already in oxide form so no calcination required for then.

Q86

In the structure of the dichromate ion, there is a :

A linear symmetrical Cr-O-Cr bond.

B non-linear symmetrical Cr-O-Cr bond.

C linear unsymmetrical Cr-O-Cr bond.

D non-linear unsymmetrical Cr-O-Cr bond.

Correct Answer

Option B

Solution

Dichromate ion contain non-linear symmetrical Cr-O-Cr bond.

Q87

Which of the following factors may be regarded as the main cause of lanthanide contraction?

A Poor shielding of one of 4f electron by another in the subshell

B Effective shielding of one of 4f electrons by another in the subshell

C Poorer shielding of 5d electrons by 4f electrons

D Greater shielding of 5d electrons by 4f electrons

Correct Answer

Option C

Solution

The main reason of lanthanide contraction is, poor shielding of 4f electrons on the outer most shell electrons.

In lanthanides, there is poorer shielding of

5d

electrons by

4f

electrons resulting in greater attraction of the nucleus over

5d

electrons and reduction of the atomic radii.

Q88

A metal,

M

forms chlorides in its

+2

and

+4

oxidation states. Which of the following statements about these chlorides is correct?

A

MC{l_2}

is more ionic than

MC{l_4}

B

MC{l_2}

is more easily hydrolysed than

MC{l_4}

C

MC{l_2}

is more volatile than

MC{l_4}

D

MC{l_2}

is more soluble in anhydrous ethanol than

MC{l_4}

.

Correct Answer

Option A

Solution

Metal atom in the lower oxidation state forms the ionic bond and in the higher oxidation state the covalent bond.

Because higher oxidation state means small size and great polarizing power and hence greater the covalent character.

Hence

MC{l_2}

is more ionic than

MC{l_4}.

Q89

5 g of zinc is treated separately with an excess of (a) dilute hydrochloric acid and (b) aqueous sodium hydroxide. The ratio of the volumes of H2 evolved in these two reactions is :

A 1 : 2

B 1 : 1

C 1 : 4

D 2 : 1

Correct Answer

Option B

Solution

Zn + 2dil.

HCl $\to$ ZnCl2 + H2 Zn + 2NaOH $\to$ Na2ZnO2 + H2 From one mole of Zn, 1 mol of H2 is produced by both NaOH and HCl.

The ratio of the volume of H2 is 1 : 1

Q90

Calgon is used for water treatment. Which of the following statement is NOT true about Calgon?

A It is also known as Graham's salt.

B It is polymeric compound and is water soluble.

C It does not remove Ca2+ ion by precipitation.

D Calgon contains the 2nd most abundant element by weight in the Earth's crust.

Correct Answer

Option D

Solution

Calgon is sodium hexametaphosphate, a polymeric compound also called as Graham’s salt.

Order of abundance of element in earth crust is O > Si > Al > Fe > Ca > Na > Mg > K So second most abundant element in earth crust is Si not Ca.