Explanation

Friedrich Wöhler synthesized urea from ammonium cyanate in 1828, marking the birth of organic chemistry.

This experiment disproved the belief that organic compounds could only be made by living organisms.

Explanation

In the solid and liquid phase, AlCl₃ forms a bridged dimer structure: Al₂Cl₆, where two Al atoms are connected via chlorine bridges.

This happens because Al³⁺ seeks stability through coordinate bonding, leading to a bridge-type (dimeric) structure.

Explanation

Sound waves are mechanical vibrations that can disturb air particles around a candle flame.

This disturbance causes the flame to flicker due to pressure variations in the air.

Explanation

Octyl acetate is a natural ester known for its fruity, orange-like aroma.

It is commonly used in flavorings and perfumes to mimic orange scent.

Explanation

Graham Edgar introduced the octane number concept in the 1920s to measure the anti-knocking quality of fuels.

He established iso-octane (100) and n-heptane (0) as reference points for rating fuels.

Explanation

Cobalt (Co) is a typical transition metal with partially filled d-orbitals, a key trait of transition elements.

It shows variable oxidation states and forms colored compounds—classic properties of transition metals.

Explanation

Methane (CH₄) is a stable greenhouse gas with a relatively long atmospheric lifetime.

Its mean residence time in the atmosphere is approximately 3 to 7 years before it reacts or breaks down.

Explanation

Cl-CH₂-COOH (chloroacetic acid) is the strongest because the electronegative chlorine atom withdraws electrons, increasing acidity.

This stabilizes the conjugate base, making it a stronger acid than formic acid (HCOOH) or acetic acid (CH₃COOH).

Explanation

NO₂ is a reddish-brown gas that gives photochemical smog its characteristic brownish color.

It is formed by the reaction of NO with oxygen in sunlight.

It is a major pollutant in urban smog.

Explanation

The reaction where larger hydrocarbons (like C₈H₁₈) break into smaller ones (like C₃H₆ and fragments) is called cracking.

Cracking is commonly used in the petroleum industry to produce smaller, more useful hydrocarbons such as alkenes and gasoline.