Which of the following reactions is a double displacement reaction? MCQ with Answer and Explanation

Explanation:
C₂H₆ (ethane) follows the general formula CnH₂n+2 (n=2 gives C₂H₆), which is the formula for alkanes. Alkanes are saturated hydrocarbons with single bonds. Alkenes have CnH₂n (e.g., C₂H₄), alkynes CnH₂n-2 (e.g., C₂H₂), alcohols have –OH group. Ethane is a component of natural gas and is used to produce ethylene. Methane (CH₄) is the simplest alkane.

Explanation:
Boyle's law: P₁V₁ = P₂V₂. Given P₁=1.0 atm, V₁=2.0 L, P₂=4.0 atm. V₂ = (1.0 × 2.0) / 4.0 = 0.5 L. Volume decreases as pressure increases, because gas is compressible. The product PV is constant for a fixed mass of gas at constant T. Scuba divers experience this; as they dive deeper, pressure increases, reducing air volume in lungs.

Explanation:
Methane (CH4) is commonly known as marsh gas because it is produced by the anaerobic decomposition of organic matter in swamps and marshes by methanogenic bacteria. It is also the primary component of biogas and natural gas.