The statement that is not correct for periodic classification of elements is:
(i) The properties of elements are periodic function of their atomic numbers.
(ii) Non metallic elements are less in number than metallic elements.
(iii) For transition elements, the 3d-orbitals are filled with electrons after 3p-orbitals and before 4s-orbitals.
(iv) The first ionisation enthalpies of elements generally increase with increase in atomic number as we go along a period.
The statement that is not correct for periodic classification of elements is:
(i) The properties of elements are periodic function of their atomic numbers.
(ii) Non metallic elements are less in number than metallic elements.
(iii) For transition elements, the 3d-orbitals are filled with electrons after 3p-orbitals and before 4s-orbitals.
(iv) The first ionisation enthalpies of elements generally increase with increase in atomic number as we go along a period.
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1 Answer
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This is a Multiple Choice Questions as classified in NCERT Exemplar
Option (iii)
As per Aufbau principle 3d orbitals are filled first than 4s as due to lower n value.
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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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