Graphite is used as an electrode because it: MCQ with Answer and Explanation

Explanation:
Biogas, commonly known as gobar gas in India, is produced by the anaerobic digestion of organic waste (like cattle dung) by methanogenic bacteria. The primary component of biogas is methane (CH4), which typically makes up 50-75% of the gas mixture, along with carbon dioxide and trace gases.

Explanation:
Gastric juice in the stomach contains hydrochloric acid (HCl) which aids digestion and kills bacteria. Orange juice contains citric acid, vinegar acetic acid, milk lactic acid (from fermentation). The pH of stomach acid is around 1-2.

Explanation:
Melting of wax is a physical change because it involves only a change in state from solid to liquid without altering the chemical composition. The wax remains the same hydrocarbon mixture. In contrast, rusting of iron (Fe₂O₃·xH₂O formation), burning of magnesium (MgO formation), and digestion of food (enzymatic breakdown into simpler molecules) are chemical changes where new substances are formed. Physical changes are reversible, while most chemical changes are irreversible. Exam tip: Remember, changes of state (melting, boiling, condensation) are physical changes unless a chemical reaction accompanies them.