The s-Block Elements

Question 209
CBSEENCH11008080

Which of the following on thermal decomposition yields a basic as well as an acidic oxide?

  • NaNO3

  • KClO3

  • CaCO3

  • NH4NO3

Solution

C.

CaCO3

CaCO subscript 3 space rightwards arrow with increment on top space CaO with Basic below space plus stack space CO subscript 2 with Acidic below
Question 210
CBSEENCH11008113

Both lithium and magnesium display several similar properties due to the diagonal relationship; however, the one which is incorrect is :

  • Both form basic carbonates

  • Both form soluble bicarbonates

  • Both form nitrides

  • Nitrates of both Li and Mg yield NO2 and O2 on heating

Solution

A.

Both form basic carbonates

Lithium can form carbonate (Li2CO3). Lithium Carbonate is not basic in nature. On other hands, Mg can form basic carbonate.
5Mg+2 + 6CO32- + 7H2O → 4 MgCO3.Mg(OH)2.5H2O + 2HCO3-

Question 211
CBSEENCH11008278

Which one of the alkali metals, forms only the normal oxide, M2O on heating in air?

  • Rb

  • K

  • Li

  • Na

Solution

C.

Li

Li is the alkali metal which forms only normal oxide Li2O when heated in air.
2Li +1/2 O2 ---> Li2O
sodium, when heated in air forms peroxide while heavier alkali metals form superoxide as the major product. 

Question 212
CBSEENCH11008293

In the replacement reaction



The reaction will be most favourable if M happens to be

  • Na

  • K

  • Rb

  • Li

Solution

C.

Rb

For the reaction,

The reaction will be faster with Rb because lattice energy of RbF is less than LiF, NaF, KF.

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