Chemical Reactions

Step 1: Understanding Metal-Acid Reactivity:
Metals that are more reactive than hydrogen (positioned above hydrogen in the reactivity series) displace hydrogen from dilute acids to produce hydrogen gas.

Step 2: Evaluating the Observations:
beginenumerate Copper (Cu): Below hydrogen in the reactivity series. It does not react with dilute HCl. (Observation 1 is Incorrect). Iron (Fe): Above hydrogen. It reacts to give (H_2) gas. (Observation 2 is Correct). Magnesium (Mg): Highly reactive, above hydrogen. It reacts vigorously to give (H_2) gas. (Observation 3 is Incorrect). Zinc (Zn): Above hydrogen. It reacts to give (H_2) gas. (Observation 4 is Correct). endenumerate

Step 3: Identifying Correct Observations:
Only observations 2 (Iron) and 4 (Zinc) accurately reflect the chemical reality.

Step 4: Final Answer:
The correct choice is Both 2 and 4.

Step 1: Understanding the Chemical Reaction:
Concentrated sulphuric acid (H_2SO_4) acts as a powerful oxidizing agent. When it reacts with elemental carbon, it oxidizes the carbon to carbon dioxide while being reduced to sulphur dioxide.

Step 2: Identifying the Product Gases:
The balanced chemical equation for the reaction is: [ C + 2H_2SO_4 (textconc.) CO_2 + 2SO_2 + 2H_2O ] The two gaseous products are Carbon dioxide (CO_2) and Sulphur dioxide (SO_2).

Step 3: Lime Water Test:
Both CO_2 and SO_2 have the property of reacting with lime water [calcium hydroxide, Ca(OH)_2] to form a white precipitate (CaCO_3 and CaSO_3 respectively), which makes the solution appear milky.

Step 4: Final Answer:
Carbon is the unique non-metal in this list that produces both of these gases simultaneously upon reaction with concentrated acid.

(a) Fluorine (F): Electronegativity increases across a period from left to right. Fluorine is the furthest to the right in Period 2 (excluding noble gases) and is the most electronegative element in the entire periodic table.

(b) Sodium (Na): Atomic size decreases across a period due to an increase in nuclear charge. Therefore, the element at the beginning of Period 3, Sodium, has the largest atomic radius in that period.

(a) ZnO: Zinc Oxide is an amphoteric oxide, meaning it reacts with both acids and strong bases (alkalis) like KOH to form salt and water. CuO is basic and does not dissolve in KOH.

(b) 2Br(^-) () Br(_2) + 2e(^-): At the anode (positive electrode), oxidation occurs. Bromide ions lose electrons to form neutral bromine atoms, which then form bromine gas molecules.

(c) 5.6 (Note: Provided options may be incorrect; 5.6 is the calculation): Molecular weight of (O_2 = 16 times 2 = 32) g. 32 g of (O_2) occupies 22.4 L at STP. 8 g of (O_2) occupies (frac22.432 times 8 = mathbf5.6) litres. Correction: If restricted to brackets, 8.96 is mathematically closest but incorrect based on standard 22.4 L molar volume.

(d) Cu: Copper is below hydrogen in the reactivity series and cannot displace hydrogen from acids. Manganese (Mn) and Magnesium (Mg) are the only two metals that react with very dilute ((1%)) (HNO_3) to evolve hydrogen.

(e) HCl: Hydrogen Chloride has a large difference in electronegativity between H and Cl, creating a partial charge (dipole). Carbon tetrachloride ((CCl_4)) is non-polar because its symmetrical tetrahedral shape causes individual bond polarities to cancel out.

(a) — 4. Redox: In this reaction, Copper Oxide is being reduced (loses oxygen) and Carbon is being oxidized (gains oxygen).

(b) — 3. Reduction: Gain of electrons is defined as reduction. Aluminum ions gain three electrons to form aluminum atoms.

(c) — 5. Electrolytic dissociation: The separation of ions of a pre-existing ionic compound (molten or aqueous) is called electrolytic dissociation.

(d) — 1. Oxidation: Loss of electrons is defined as oxidation. Oxide ions lose electrons at the anode to form oxygen gas.

(e) — 2. Ionization: The process by which a polar covalent compound (like gaseous HCl) forms ions when dissolved in water.

(a) A compound which reacts with water to give acetylene gas:
Calcium Carbide (CaC_2).
The reaction is: CaC_2 + 2H_2O Ca(OH)_2 + C_2H_2uparrow

(b) The gas evolved when sodium propanoate is heated with soda lime:
Ethane (C_2H_6).
This is a decarboxylation reaction: C_2H_5COONa + NaOH xrightarrowCaO, Delta C_2H_6 + Na_2CO_3.

(c) A reddish-brown precipitate formed when ferric chloride solution reacts with an alkali:
Ferric Hydroxide [Fe(OH)_3].
The reaction with sodium hydroxide is: FeCl_3 + 3NaOH Fe(OH)_3downarrow + 3NaCl.

(d) A pair of electrons present in an atom which is not shared with any other atom during bond formation:
Lone pair (or unshared pair).

(e) The relative molecular mass of a substance expressed in grams:
Gram Molecular Mass (or one mole).