Periodic Trends In Properties Of Elements

The elements Ge, Sn, Pb are in Group 14 (Carbon family).
Order down the group: C, Si, Ge, Sn, Pb.

Option (1): Ionization Enthalpy (IE):
General trend: Ionization Enthalpy (IE) decreases down a group due to increasing atomic size and shielding effect.
Expected order: .
The stated order is consistent with the general trend.
However, there can be irregularities.
The first IE values (kJ/mol) are:
Ge: 762, Sn: 709, Pb: 716.
So, the actual order is .
Therefore, the stated order is incorrect.

Option (2): Melting Point:
Melting points generally decrease down this group for C, Si, Ge.
But then Sn and Pb have lower melting points due to weaker metallic bonding (d- and f-orbital effects, inert pair effect influences bonding character).
Melting points (in K):
C (diamond): ~3823 K, Si: 1687 K, Ge: 1211 K, Sn: 505 K, Pb: 601 K.
So the order of melting points is .
The stated order is correct.

Option (3): Density:
Density generally increases down a group due to increasing atomic mass and similar packing efficiency or decreasing atomic volume change relative to mass change.
Densities (g/cm ):
Ge: 5.32, Sn: 7.31 (white tin), Pb: 11.34.
So the order of density is .
The stated order is correct.

Option (4): Electrical Resistivity:
Metals generally have low resistivity (high conductivity). Non-metals have high resistivity. Metalloids are in between.
Down Group 14, metallic character increases: Ge (metalloid/semiconductor) < Sn (metal) < Pb (metal).
Resistivity values ( at 20°C):
Ge: (semiconductor), Sn: , Pb: .
So, for metals Sn and Pb, Pb has slightly higher resistivity than Sn.
Ge (semiconductor) has much higher resistivity than both.
The order of resistivity is .
The stated order is correct.

Conclusion:
The incorrect order is (1) for Ionization Enthalpy.
The correct order is .
Therefore, the answer is .

The elements Ge, Sn, Pb are in Group 14 (Carbon family).
Order down the group: C, Si, Ge, Sn, Pb.

Option (1): Ionization Enthalpy (IE):
General trend: Ionization Enthalpy (IE) decreases down a group due to increasing atomic size and shielding effect.
Expected order: .
The stated order is consistent with the general trend.
However, there can be irregularities.
The first IE values (kJ/mol) are:
Ge: 762, Sn: 709, Pb: 716.
So, the actual order is .
Therefore, the stated order is incorrect.

Option (2): Melting Point:
Melting points generally decrease down this group for C, Si, Ge.
But then Sn and Pb have lower melting points due to weaker metallic bonding (d- and f-orbital effects, inert pair effect influences bonding character).
Melting points (in K):
C (diamond): ~3823 K, Si: 1687 K, Ge: 1211 K, Sn: 505 K, Pb: 601 K.
So the order of melting points is .
The stated order is correct.

Option (3): Density:
Density generally increases down a group due to increasing atomic mass and similar packing efficiency or decreasing atomic volume change relative to mass change.
Densities (g/cm ):
Ge: 5.32, Sn: 7.31 (white tin), Pb: 11.34.
So the order of density is .
The stated order is correct.

Option (4): Electrical Resistivity:
Metals generally have low resistivity (high conductivity). Non-metals have high resistivity. Metalloids are in between.
Down Group 14, metallic character increases: Ge (metalloid/semiconductor) < Sn (metal) < Pb (metal).
Resistivity values ( at 20°C):
Ge: (semiconductor), Sn: , Pb: .
So, for metals Sn and Pb, Pb has slightly higher resistivity than Sn.
Ge (semiconductor) has much higher resistivity than both.
The order of resistivity is .
The stated order is correct.

Conclusion:
The incorrect order is (1) for Ionization Enthalpy.
The correct order is .
Therefore, the answer is .