Question 1

Choose a false statement regarding the properties of sodium hydroxide.

Accepted Answer

Sodium hydroxide ( NaOH ) is a strong base. Basic solutions turn red litmus paper blue. Therefore, the statement that the solution of NaOH turns blue litmus red is false. The other statements are true: NaOH is highly soluble in water. It reacts with atmospheric CO _2 to form sodium carbonate ( Na _2 CO _3). It is a white, deliquescent solid that readily absorbs moisture from the air. Answer: the solution of NaOH turns blue litmus red.

Question 2

Which element from following forms superoxide with oxygen?

Accepted Answer

Alkali metals react with oxygen to form different types of oxides depending on their size. Lithium forms mainly monoxide (Li_ 2 O). Sodium forms mainly peroxide (Na_ 2 O_ 2 ). Potassium, rubidium, and cesium form mainly superoxides (MO_ 2 ) due to the stabilization of the large superoxide ion by large cations. Magnesium forms mainly monoxide (MgO). Therefore, potassium forms a superoxide with oxygen. Answer: Potassium

Question 3

What is the general formula of halide salts of alkali metals if M is a metal atom ?

Accepted Answer

Alkali metals belong to Group 1 of the periodic table and have one valence electron. They lose this electron to form a unipositive ion, M^ + . Halogens belong to Group 17 and have seven valence electrons. They gain one electron to form a uninegative ion, X^ - . To form a neutral salt, one M^ + ion combines with one X^ - ion. The general formula of halide salts of alkali metals is MX. Answer: MX

Question 4

Which from the following metal chlorides does not contain water of crystallisation ?

Accepted Answer

Alkali metal chlorides generally do not form hydrates, with the exception of lithium chloride, which is deliquescent and crystallises as a dihydrate, LiCl 2 H _2 O . Alkaline earth metal chlorides such as MgCl _2 and BeCl _2 readily form hydrates. MgCl _2 crystallises as a hexahydrate, MgCl _2 6 H _2 O , and BeCl _2 crystallises as a tetrahydrate, BeCl _2 4 H _2 O . Caesium chloride ( CsCl ) is an alkali metal chloride that does not form hydrates and crystallises as an anhydrous salt. Therefore,

Question 5

Which of the following compounds is formed when chlorine reacts with dry slake lime Ca(OH) _2 ?

Accepted Answer

When chlorine gas is passed over dry slaked lime Ca(OH) _2, bleaching powder is formed. The chemical reaction is given by: Ca(OH) _2 + Cl _2 CaOCl _2 + H _2 O The compound formed is CaOCl _2. Answer: CaOCl _2

Question 6

Identify the alkali metal having the smallest atomic size from following.

Accepted Answer

The alkali metals given in the options belong to Group 1 of the periodic table. As we move down a group, the number of electron shells increases, which leads to an increase in atomic size. The order of the given alkali metals from top to bottom in Group 1 is Sodium (Na), Potassium (K), Rubidium (Rb), and Caesium (Cs). Therefore, the order of their atomic sizes is Na Among the given options, Sodium has the smallest atomic size. Answer: Sodium

Question 7

Identify the elements of alkali metals and alkaline earth metals respectively having highest 1st ionization enthalpy.

Accepted Answer

Ionization enthalpy decreases down a group in the periodic table due to an increase in atomic size and shielding effect. Among alkali metals (Group 1), Lithium ( Li ) is at the top of the group and has the smallest atomic size, hence it has the highest first ionization enthalpy. Among alkaline earth metals (Group 2), Beryllium ( Be ) is at the top of the group and has the smallest atomic size, hence it has the highest first ionization enthalpy. Therefore, the elements with the highest first ioni

Question 8

Which alkaline earth metal carbonate decomposes most easily?

Accepted Answer

The thermal stability of alkaline earth metal carbonates increases down the group from Be to Ba. This is because as the size of the cation increases, its polarizing power decreases. A smaller cation like Mg^ 2+ polarizes the large carbonate ion (CO_3^ 2- ) more effectively, weakening the C-O bond and facilitating its decomposition into the metal oxide and CO_2. The order of thermal stability is MgCO_3 Therefore, MgCO_3 has the lowest thermal stability among the given options and decomposes most

s Block Elements — Previous Year Questions & Solutions