NEET

he volatile metal is :

Fe
Zn
Cu
Ag

Solution

Zn is volatile meta

Copper and con. H₂SO₄ react to produce

Cu
SO₂
H₂
O₂

Solution

Copper reacts with H₂SO₄ to produce SO₂

Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O

But Cu does not displace H₂ from dilute H₂SO₄ as it is less reactive than H₂(comes below H₂ in electrochemical series)

For the ions Zn²⁺, Ni²⁺ and Cr³⁺ which among the following statements is correct?(atomic number of Zn = 30, Ni = 28 and Cr = 24)

All these are colourless
All these are coloured
Only Ni²⁺ is coloured and Zn²⁺ and Cr³⁺ are colourless
Only Zn²⁺ is colourless and Ni²⁺ and Cr³⁺ are coloured

Solution

The ions with unpaired electrons are colourled and those with paired electrons are colourless.

\(\underset{No.\, of\, e^{-}s=28}{Zn^{2+}}=1s^{2},2s^{2}p^{6}d^{10}\)

\(\underset{No.\, of\, e^{-}s=21}{Cr^{3+}}=1s^{2},2s^{2}p^{6}d^{3}\)

\(\underset{No.\, of\, e^{-}s=26}{Cr^{2+}}=1s^{2},2s^{2}p^{6}d^{8}\)

Thus Zn²⁺,Cr³⁺ and Ni²⁺ have zero, 3 and 2 unpaired electrons respectively.

Which of the following ions has the maximum magnetic moment?

Mn⁺²
Fe⁺²
Ti³⁺
Cr⁺²

Solution

Mn⁺⁺ –5 unpaired electrons

Fe⁺⁺ – 4 unpaired electrons

Ti⁺⁺ – 2 unpaired electrons

Cr⁺⁺ – 4 unpaired electrons Hence maximum no. of unpaired electron is present in Mn⁺⁺.

Magnetic moment α number of unpaired electrons

In which of the following pairs both the ions are coloured in aqueous solutions ?

(At.no. : Sc = 21,Ti= 22, Ni = 28, Cu = 29, Co = 27)

Sc³⁺, Ti³⁺
Sc³⁺, Co²⁺
Ni²⁺, Cu+
Ni²⁺, Ti³⁺

Solution

Sc³⁺ : 1s², 2s²p⁶, 3s²p⁶d⁰, 4s⁰; no unpaired electron.

Cu⁺: 1s², 2s²p⁶, 3s¹⁰p⁶d⁶, 4s⁰; no unpaired electron.

Ni²⁺: 1s², 2s²p⁶, 3s²p⁶d⁸, 4s⁰;unpaired electrons are present.

Ti³⁺ : 1s², 2s²p⁶, 3s²p⁶d¹, 4s⁰;unpaired electron is present

Co²⁺ : 1s², 2s²p⁶, 3s²p⁶d⁷, 4s⁰;unpaired electrons are present So from the given options the only correct combination is Ni²⁺ and Ti³⁺

When tin is treated with concentrated nitric acid:

it is converted into stannous nitrate
it is converted into stannic nitrate
it is converted into metastannic acid
it becomes passive

Solution

Tin on reaction with conc. HNO₃ to form meta stannic acid and nitrogen dioxide.
\(\underset{tin}{Sn}+\underset{nitric\, acid\, (conc.)}{4HNO_{3}}\rightarrow \underset{Meta\, stannic\, acid}{H_{2}SnO_{3}}+\underset{nitrogen\, dioxide}{4NO_{2}}+H_{2}O\)

The aqueous solution containing which one of the following ions will be colourless? (Atomic number:Sc = 21, Fe = 26, Ti = 22, Mn = 25)

Sc³⁺
Fe²⁺
Ti³⁺
Mn²⁺

Solution

In Sc³⁺ there is/are no unpaired electrons. So the aqueous solution of Sc³⁺ will be colourless.

Which one of the following ionic species will impart colour to an aqueous solution?

Ti⁴⁺
Cu⁺
Zn²⁺
Cr³⁺

\(4K_{2}Cr_{2}O_{7}\overset{heat}{\rightarrow}4K_{2}CrO_{4}+3O_{2}+X\). In the above reaction X is:

CrO₃
Cr₂O₇
Cr₂O₃
CrO₅

Solution

Potassium dichromate dissociates with evolution of O₂ on heating.

4 K₂Cr₂O₇ → 4 K₂CrO₄ + 2Cr₂O₃ + 3O₂

So, X is Cr₂O₃

The oxides, CrO₃, MoO₃, and WO₃ are strongly

neutral
acidic
basic
none of these

Solution

The transition metal oxides in which metal is in lower oxidation states are basic and in which metal is in higher oxidation states are acidic while with intermediate oxidation states are amphoteric.

\(\overset{+6}{CrO_{3}}\: \overset{+6}{MoO_{3}}\: \overset{+6}{WO_{3}}\)

So, the given transition metal oxides are acidic in nature.

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