Periodic Table and Elements

Cesium (Cs) forms a stable superoxide (CsO₂) due to its large ionic radius, which can stabilize the larger superoxide ion (O₂⁻). Among alkali metals, the stability of superoxides increases down the group - potassium, rubidium, and cesium form superoxides, while lithium forms only the oxide and sodium forms primarily the peroxide. Ba is an alkaline earth metal.

Diagonal relationships exist between elements diagonally adjacent in the periodic table: Li-Mg (1st period, 1st group to 2nd period, 2nd group), Be-Al (2nd period, 2nd group to 3rd period, 3rd group), and B-Si (2nd period, 3rd group to 3rd period, 4th group). Li-Be are in the same period and do NOT show diagonal relationship.

Beryllium (Be) predominantly forms covalent compounds due to its very small atomic size and high ionization energy, which gives it high polarizing power (Fajan's rules). This allows Be to distort electron clouds of anions and form electron-sharing bonds rather than pure ionic bonds. Mg, Cs, and Na typically form ionic compounds.

Cesium (Cs) does not form a stable nitride due to its very large ionic radius and low charge density, which makes ionic bonding with N^3- unfavorable. Li, Mg, and Al readily form nitrides (Li3N, Mg3N2, AlN) due to their smaller size and higher charge density allowing stable ionic interactions.

Alkali metals have large size, which cannot fit into the interstitial sites.

Alkaline earth metals (Group 2: Be, Mg, Ca, Sr, Ba, Ra) have higher melting and boiling points than alkali metals (Group 1: Li, Na, K, Rb, Cs, Fr). This is because alkaline earth metals have TWO valence electrons, forming stronger metallic bonds with higher bond energies. Their smaller atomic radii and higher charge density contribute to this increased strength of metallic bonding compared to the single-bonded alkali metals.

The work function of zinc is 4.24 eV.

Ans : 2.

Ans : 4.

For the sulphates of alkaline earth metals, the cations are much smaller than the anions. On moving down the group, the change in size of the cations does not cause a significant change in ∆H_lattice, but ∆H_hydration becomes less negative. As a result, ∆H_solution becomes less negative and the solubility of alkaline earth metal sulphates decreases down the group. For the hydroxides of alkaline earth metals, the size of the anions and cations are of the same order of magnitude. On moving down the group, less energy is required to break the lattice as the size of cations increases, but the change in ∆H_hydration is comparatively small. Consequently, the ∆H_solution becomes more negative and the solubility of alkaline earth metal hydroxides increases down the group.

Because their atoms are significantly smaller than those of alkali metals, alkaline earth metals have higher densities. Alkaline earth metal ions are much smaller in size than corresponding alkali metal ions and carry a higher charge. Thus, their polarizing power is greater. Electron cloud of carbonate anions are more easily distorted by alkaline earth metal ions than by alkali metal ions. Therefore, alkaline earth metal carbonates are less stable to heat and decompose to form metal oxide and carbon dioxide. Thus, this option is wrong. This option is correct because melting points in alkaline earth metals are higher than for the corresponding alkali metals. Alkaline-earth metals contribute two electrons per atom to the mobile electron cloud whereas alkali metals contribute only one electron per atom. The greater number of electrons and the smaller ionic size of the alkaline earth metals helps to increase the density of the electron cloud and thus increase the attractive forces between the mobile electrons and the cationic lattice. Alkaline earth metal ions are much smaller in size than corresponding alkali metal ions and carry a higher charge. Thus, their polarizing power is greater. Electron cloud of carbonate anions are more easily distorted by alkaline earth metal ions than by alkali metal ions. Therefore, alkaline earth metal carbonates are less stable to heat and decompose to form metal oxide and carbon dioxide.

The hydration enthalpies of alkali metal ions decrease with increase in ionic sizes. The correct order of hydration enthalpies of alkali metal ions is Li+> Na+ > K+ > Rb+ > Cs+. The thermal stability of alkali metal hydrides decreases from LiH to CsH.

Ionisation potential increases as we move from the left to the right of a period and decreases as we move down a group. Sodium is on the extreme left of period 3. Hence, it has the least ionisation potential as compared to the elements of the first three periods.

The third period in the modern periodic table consists of the elements sodium, magnesium, aluminium, silicon, phosphorous, sulphur, chlorine and argon, in that order. The given elements belong to the third period. As we move from left to right of a period, the ionisation potential increases. Hence, sodium has the least ionisation potential and chlorine has the highest. So, the fifth option is correct.

Correct order of melting points is potassium (336 K) < sodium (371 K) < magnesium (924 K) < calcium (1124 K).