Assertion (A) : Boron has a smaller first ionisation enthalpy than beryllium.
Reason (R)
: The penetration of a 2s electron to the nucleus is more than the 2p electron hence 2p electron is more shielded by the inner core of electrons than the 2s electrons.
(i) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(ii) Assertion is correct statement but reason is wrong statement.
(iii) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(iv) Assertion and reason both are wrong statements
Assertion (A) : Boron has a smaller first ionisation enthalpy than beryllium.
Reason (R) : The penetration of a 2s electron to the nucleus is more than the 2p electron hence 2p electron is more shielded by the inner core of electrons than the 2s electrons.
(i) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(ii) Assertion is correct statement but reason is wrong statement.
(iii) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(iv) Assertion and reason both are wrong statements
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1 Answer
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This is a Assertion and Reason Type Questions as classified in NCERT Exemplar
Option (iii)
The Be has the electronic configuration of [He]2s2 while B has the electronic configuration of [He]2s22p1 . As in Be the outermost orbital i.e. 2s is fully filled thus it provides extra stability to the Be compared to B. Apart from this 2s electron is more penetrated compared to the 2p electron for which 2p electron faces more shielding effect than that of 2s electron.
Similar Questions for you
Among isoelectronic monoatomic species, size is inversely proportional to atomic number. Hence among isoelectronic species Na? , O²? , N³? , F? (having the nearest noble gas configuration);
Order of size is Na? < F? < O²? < N³?
N³? has least atomic number hence the largest size
Electron gain enthalpy increases with electro negativity chlorine has higher electron gain enthalpy than fluorine (exception)
In isoelectronic species nuclear charge can be approximated as
Nuclear charge ≈ z / no. of electrons
Al³? Mg²? Na? F? O²? N³?
Nuclear Charge: 13/10 12/10 11/10 9/10 8/10 7/10
Minimum nuclear charge is in N³? and maximum is in Al³?
So order should be
Al³? < Mg²? < Na? < F? < O²? < N³?
(a) The element V has the highest first ionization enthalpy (? iH1) and positive electron gain enthalpy (? egH) and hence it is the least reactive element. Since inert gases have positive? egH, therefore, the element-V must be an inert gas. The values of? iH1, ? iH2 and? egH match that of He.
(b) The element II which has the least first ionization enthalpy (? iH1) and a low negative electron gain enthalpy (? egH) is the most reactive metal. The values of ? iH1, ? iH2 and? egH match that of K (potassium).
(c) The element III which has high fi
This is a Matching Type Questions as classified in NCERT Exemplar
i d + 48
ii a &n
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