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NEET Practice Questions (MCQs) with Answers & Solutions

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Borax is prepared by treating colemanite with:

$N a N O_{3}$

NaCl

$N a_{2} C O_{3}$

$N a H C O_{3}$

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Explanation

Borax (Na2B4O7.10H2O) is prepared by treating the mineral colemanite (Ca2B6O11.5H2O) with a hot solution of sodium carbonate (Na2CO3). The calcium ions are precipitated as calcium carbonate, leaving sodium tetraborate in solution.

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The correct Lewis acid order for boron halides is:

$B F_{3} > B C l_{3} > B B r_{3} > B I_{3}$

$B C l_{3} > B F_{3} > B B r_{3} > B I_{3}$

$B I_{3} > B B r_{3} > B C l_{3} > B F_{3}$

$B B r_{3} > B C l_{3} > B I_{3} > B F_{3}$

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Explanation

due to back bonding ,electron density increase on BF₃ , so acidic character decreases.due to larger size of I , extent of back bonding decrease.

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The main factor responsible for weak acidic nature of B-F bonds in $B F_{3}$ is:

large electronegativity of F

three centred two electrons bonds in $B F_{3}$

px- $d π$ back bonding

$p π - pπ$ back bonding

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Explanation

BF3 shows strong pπ-pπ back bonding.
- This double bond character explains electron deficiency in BF3.
- Therefore, BF3 is less likely to donate electrons and acts as weak lewis acid.

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Which of the following is a gas?

$B F_{3}$

$B C l_{3}$

$B B r_{3}$

$B I_{3}$

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Explanation

BF₃ is gas because there is a back donation of electron from fluorine to boron therefore molecular association does not take place. As the size of halogen increases, back donation property decreases and molecular association increases therefore BCl

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B-F bond order in $B F_{3}$ is:

4/3

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Aluminium reacts with nitrogen to form:

AlN

$A l_{2} N_{3}$

$A l_{2} N$

$A l_{4} N_{6}$

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Explanation

Aluminium react with nitrogen to produce aluminium nitride(Aln). This reaction takes place at a temperature of 800-1200°C. Aluminium has a higher affinity for oxygen than nitrogen, and so in the presence of oxygen and nitrogen will form Al 2O 3 in preference to AlN.

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Which metal is powdered, suspended in oil and used as paint?

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Explanation

The reflective property of aluminium is being used here. Powdered aluminium suspended in oil is used as paint. The low cost and easy availability make it useful in this.

This compound is also known as Diaspore having formula

A l_{2} O_{3} . H_{2} O

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Aluminium metal is corroded in coastal places near to the sea, because protective oxide film:

is removed by sea water

reacts with sea water

is attacked by salts present in sea water

reacts with sand particles

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Explanation

The presence of salt (or any electrolyte) in the water accelerates the reaction because it increases the conductivity of water, effectively increasing the concentration of ions in the water and so increasing the rate of oxidation (corrosion) of the metal.

Thusm aluminium metal is corroded in places that are near to the sea.

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Aluminium deposited as vapours on glass forms a good mirror, essentially because:

it has better shine than Ag

it does not scratch

coating is much smoother

it does not tarnish in air

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Explanation

Aluminium, deposited as vapour on a glass, forms good mirrors because it does not tarnish in air. If it tarnishes then the mirror would not be that good. Hence due to the property of it not tarnishing in air the mirror formed are good mirrors

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Conc. $H N O_{3}$ can be stored in a container of:

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Explanation

(i) Conc. $H N O_{3}$ can be transported in an aluminum container because the reaction between Al and nitric acid forms a thin layer of oxide on the aluminum surface which makes it passive.

Nitric acid reacts with aluminium and forms a protective layer i.e. Al2O3. This protective layer makes aluminium unreactive towards HNO3 and therefore, it can be stored in aluminium containers.

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