### Related Formula Group 13 elements (mathrmB, mathrmAl, mathrmGa, mathrmIn, mathrmTl$\mathrm{B}, \mathrm{Al}, \mathrm{Ga}, \mathrm{In}, \mathrm{Tl}$) show highly anomalous periodic trends due to the intervention of filled d-orbitals (d-block contraction in mathrmGa$\mathrm{Ga}$) and f-orbitals (lanthanoid contraction in mathrmTl$\mathrm{Tl}$). ### Core Logic Evaluate each specified trend against official physical constants: - **Atomic radius**: Due to d-block contraction, gallium (mathrmGa$\mathrm{Ga}$) is smaller than aluminum (mathrmAl$\mathrm{Al}$): textRadius (pm): mathrmB(88) < mathrmGa(135) < mathrmAl(143) < mathrmIn(167) < mathrmTl(170)$\text{Radius (pm): } \mathrm{B}(88) < \mathrm{Ga}(135) < \mathrm{Al}(143) < \mathrm{In}(167) < \mathrm{Tl}(170)$ Hence, the given order is *Incorrect*. - **Electronegativity**: Electronegativity first decreases from mathrmB$\mathrm{B}$ to mathrmAl$\mathrm{Al}$, then increases down the group due to poor shielding of d and f electrons: textElectronegativity: mathrmAl(1.5) < mathrmGa(1.6) < mathrmIn(1.7) < mathrmTl(1.8) < mathrmB(2.0)$\text{Electronegativity: } \mathrm{Al}(1.5) < \mathrm{Ga}(1.6) < \mathrm{In}(1.7) < \mathrm{Tl}(1.8) < \mathrm{B}(2.0)$ Hence, this order is *Correct*. ### Step 1: Analyze density and ionization energy trends - **Density**: Increases down the group as atomic mass increases much faster than atomic volume: textDensity (g/cm^3text): mathrmB(2.35) < mathrmAl(2.70) < mathrmGa(5.90) < mathrmIn(7.31) < mathrmTl(11.85)$\text{Density (g/cm}^3\text{): } \mathrm{B}(2.35) < \mathrm{Al}(2.70) < \mathrm{Ga}(5.90) < \mathrm{In}(7.31) < \mathrm{Tl}(11.85)$ Hence, the given order is *Incorrect* (it is completely reversed). - **1^mathrmst$1^{\mathrm{st}}$ Ionisation Energy**: Shows an irregular trend due to ineffective shielding by d and f electrons: textIE_1mathrm~(kJ/mol): mathrmIn(558) < mathrmAl(577) < mathrmGa(579) < mathrmTl(589) < mathrmB(801)$\text{IE}_1\mathrm{~(kJ/mol): } \mathrm{In}(558) < \mathrm{Al}(577) < \mathrm{Ga}(579) < \mathrm{Tl}(589) < \mathrm{B}(801)$ Hence, this order is *Correct*. ### Step 2: Conclusion Only the Electronegativity (B) and 1^mathrmst$1^{\mathrm{st}}$ Ionisation Energy (D) orders are correct, matching Option (1). ### Pattern Recognition Group 13 elements do not follow monotonic trends. The poor shielding of 3d^10$3d^{10}$ and 4f^14$4f^{14}$ electrons increases the effective nuclear charge on valence electrons, causing anomalies in atomic radius (mathrmGa < mathrmAl$\mathrm{Ga} < \mathrm{Al}$) and pulling electronegativities and ionization energies upward as you go further down. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: The p-Block Elements Class 11 Chemistry: Classification of Elements and Periodicity in Properties

### Core Logic Let us check the trends for the provided main group elements (mathrmAl, In, Tl$\mathrm{Al, In, Tl}$ from Group 13 and mathrmGe, Sn, Pb$\mathrm{Ge, Sn, Pb}$ from Group 14): - **Highest First Ionization Enthalpy (mathrmIE_1$\mathrm{IE}_1$):** Out of these options, Germanium (mathrmGe$\mathrm{Ge}$) sits highest and further right along its period layout, demonstrating the highest mathrmIE_1$\mathrm{IE}_1$ value among this set. Its most stable oxidation state is **+4$+4$**. - **Lowest First Ionization Enthalpy (mathrmIE_1$\mathrm{IE}_1$):** Indium (mathrmIn$\mathrm{In}$) lies lowest leftward among these relative coordinates, maintaining the lowest mathrmIE_1$\mathrm{IE}_1$. Its most stable group oxidation state is **+3$+3$** (as the inert pair effect is much more pronounced for the heavier element mathrmTl$\mathrm{Tl}$ which prefers +1$+1$). ### Pattern Recognition Sees: mathrmIE_1$\mathrm{IE}_1$ extrema vs stable oxidation state profiles. Trap: Forgetting that inert pair shifts display max stability values at +1$+1$ for mathrmTl$\mathrm{Tl}$ and +2$+2$ for mathrmPb$\mathrm{Pb}$, while lighter counterparts like mathrmIn$\mathrm{In}$ favor +3$+3$ and mathrmGe$\mathrm{Ge}$ favors +4$+4$. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: The p-Block Elements Class 12 Chemistry: The p-Block Elements

### Core Logic - **Statement I is correct:** Moving left-to-right across a period from Group 13 to Group 14 increases the effective nuclear charge (Z_texteff$Z_{\text{eff}}$) and decreases the atomic radius. Consequently, more energy is required to extract an electron, so Group 14 elements exhibit higher first ionisation enthalpies. - **Statement II is incorrect:** Group 14 elements (like Carbon, Silicon, Germanium) build robust, highly stable three-dimensional covalent network crystal structures. As a result, the melting and boiling points of Group 14 elements are generally much higher than those of the corresponding Group 13 elements. ### Pattern Recognition Covalent network solids (Group 14) create huge upward steps in phase transition energy compared to Group 13 frameworks (e.g., Gallium, which melts at nearly room temperature). ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: The p-Block Elements

### Related Formula textGroup 13 Ionisation Enthalpy Order: B > Tl > Ga > Al > In$\text{Group 13 Ionisation Enthalpy Order: } B > Tl > Ga > Al > In$ ### Core Logic The first ionisation enthalpy trend for Group 13 elements is irregular due to poor shielding by d and f electrons: - **Boron (B)** is the smallest atom in the group with no d-orbital shielding issues, so it has the **highest** ionisation enthalpy. - As we move down, poor shielding by 3d$3d$ electrons causes a slight increase at Gallium (Ga$Ga$). Poor shielding by 4f$4f$ electrons causes a sharp increase at Thallium (Tl$Tl$). - **Indium (In)** ends up with the weakest effective attraction for its outermost valence electron, giving it the **lowest** first ionisation enthalpy. Therefore, the highest and lowest elements are **B & In** respectively. ### Pattern Recognition Group 13 does not follow a linear downward trend. Remember the characteristic 'W' shape or zig-zag pattern of its ionisation energies. Indium sits at the absolute minimum point of this curve. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: The p-Block Elements