Periodic Table

Step 1: Understanding Ion Formation:
The equation (X X^2-) implies that the atom X accepts 2 electrons to form a negatively charged ion (anion).

Step 2: Applying the Octet Rule:
Non-metals gain electrons to complete their valence shell (usually reaching 8 electrons). An atom that gains 2 electrons must have had 6 valence electrons in its neutral state.

Step 3: Checking the Atomic Numbers:
16 (Sulphur): 2, 8, 6. (Needs 2 electrons to become 2, 8, 8). Matches. 10 (Neon): 2, 8. (Noble gas, stable). 12 (Magnesium): 2, 8, 2. (Loses 2 electrons to form (Mg^2+)). 14 (Silicon): 2, 8, 4. (Usually forms covalent bonds).

Step 4: Final Answer:
The atomic number is 16.

Step 1: Identifying the Element:
The total number of electrons is 2 + 8 + 2 = 12. The element with atomic number 12 is Magnesium (Mg).

Step 2: Determining Valency:
Magnesium has 2 electrons in its outermost shell. To achieve stability, it loses these 2 electrons to form a divalent cation, Mg^2+.

Step 3: Writing the Hydroxide Formula:
Hydroxide is a radical with a valency of 1 (OH^-). To balance the Mg^2+ ion, two OH^- ions are required. The chemical formula is Mg(OH)_2.

Step 4: Final Answer:
Upon dissociation, one molecule of Mg(OH)_2 produces 2 hydroxyl ions.

Step 1: Understanding Ionic Bonding:
An ionic bond is formed by the complete transfer of electrons from a metallic element (electropositive) to a non-metallic element (electronegative).

Step 2: Analyzing the Pairs:
Pair P: Both Group 1 and Group 2 are metals. Two metals do not form ionic bonds with each other.

Pair Q: Elements of Group 14 (like Carbon) and Group 16 (like Oxygen) are both non-metals and typically form covalent bonds.

Pair R: Group 2 (Metals) and Group 17 (Non-metals/Halogens) have a high difference in electronegativity, leading to ionic bond formation (e.g., MgCl_2).

Pair S: Group 18 consists of noble gases which are chemically inert and rarely form bonds.

Step 3: Conclusion:
The combination of a metal from Group 2 and a non-metal from Group 17 results in a stable ionic compound.

Step 4: Final Answer:
The correct pair is R.

(a) Reason for Caustic Soda: Caustic soda (Sodium Hydroxide) is added because aluminium oxide is amphoteric. It reacts with the hot concentrated alkali to form soluble Sodium Meta-aluminate, while the main impurities in bauxite (like Ferric Oxide) are basic and do not dissolve, allowing them to be filtered out as "red mud."

(b) Balanced Equation: [ Al_2O_3 cdot 2H_2O + 2NaOH 2NaAlO_2 + 3H_2O ] (Bauxite reacts with sodium hydroxide to produce sodium meta-aluminate and water).

(a) Storage Error: Anil should have stored the nitric acid in an amber-colored (dark) bottle and kept it in a cool, dark place away from sunlight.

(b) Thermal Decomposition: Nitric acid is unstable in the presence of heat or sunlight. It decomposes to give nitrogen dioxide (NO_2), which appears as brown fumes and dissolves in the remaining acid to give it a yellow tint. [ 4HNO_3 xrightarrowtextsunlight 4NO_2 uparrow + O_2 uparrow + 2H_2O ]

(c) Removal of Yellow Tinge: The yellow color can be removed by bubbling dry air or carbon dioxide through the acid (to drive out the dissolved NO_2) or by adding a small amount of water.

(a) False: Isomers are compounds that have the same molecular formula but different structural formulas.

(b) True: This is the chemical definition of a salt. For example, replacing H^+ in H_2SO_4 with Na^+ gives NaHSO_4 (partial replacement) or Na_2SO_4 (complete replacement).

(a) Identification: An element in Period 2 has 2 shells. Group 15 indicates 5 valence electrons. The element is Nitrogen (N) (Atomic number 7, configuration 2, 5).

(b) Formula: Nitrogen requires 3 electrons to complete its octet, and Hydrogen has 1 electron. The compound formed is Ammonia (NH_3).

(c) Electron Dot Structure: The Nitrogen atom (center) shares three of its five valence electrons with three Hydrogen atoms, leaving one lone pair.