Matching logic:

• Acetaldehyde (CH$_3$CHO): Aliphatic aldehyde — gives silver mirror with Tollen's reagent (P).
• Benzaldehyde (PhCHO): Aromatic aldehyde — forms addition compound with NaHSO$_3$ (R) (bisulphite addition).
• Cyclohexanol: Secondary alcohol — reacts with Lucas reagent (Q) (ZnCl$_2$/HCl) to form turbid chloride (within minutes).
• Phenol: Gives characteristic violet colour with FeCl$_3$ (S).

Correct: (A)→(P), (B)→(R), (C)→(Q), (D)→(S)

• $NH_{4}NO_{2} \xrightarrow{\Delta} N_{2} + 2H_{2}O$
• $Ba(N_{3})_{2} \xrightarrow{\Delta} Ba + 3N_{2}$
• $(NH_{4})_{2}Cr_{2}O_{7} \xrightarrow{\Delta} N_{2} + Cr_{2}O_{3} + 4H_{2}O$
• $(NH_{4})_{2}SO_{4}$ decomposes to release $NH_{3}$ (Ammonia) gas, not $N_{2}$.

David Berlo's SMCR (Source-Message-Channel-Receiver) Model places heavy emphasis on the communication skills of both the source/encoder and the receiver/decoder. According to Berlo:

• Encoding skills (producing messages): Speaking and Writing
• Decoding skills (receiving messages): Listening and Reading
• Skill common to both encoding and decoding: Thought or Reasoning — the intellectual capacity to analyse intentions and translate them into appropriate language or interpret received language accurately

Berlo also stressed the dyadic (two-party, relationship-based) nature of communication: the same skill level in a source might succeed with one receiver but fail with another because the receiver's skill, knowledge, attitude, and socio-cultural background differ. This makes fidelity — the degree to which the received message matches the intended message — the key measure of communication quality.

The textbook makes a philosophically profound point about the temporal dimensions of communication effects: “Effects of communication are not limited to present day activities but as a matter of fact they go beyond the limits of time and space.” The primary example given is scientific discovery: many scientists who theorised about electromagnetic waves in the 19th century could not prove their theories in their lifetimes, yet they communicated their ideas through publications. Other scientists built on this accumulated communication, eventually enabling inventions like radio. This illustrates how a single communicative act (a scientist's paper, an artist's manuscript, a philosopher's treatise) can have effects across centuries. The textbook gives another example: a medical researcher sharing a small discovery that, through the global communication network, reaches scientists thousands of miles away and contributes to a cure for a disease. Communication, therefore, is cumulative across time and space.

The Sukkur Barrage, also known as Lloyd Barrage, built across the Indus River in Sindh and completed in 1932, was the first major barrage constructed in Pakistan.