Which of the following is a metalloid? MCQ with Answer and Explanation

Explanation:
Washing soda (Na₂CO₃) reacts with Ca²⁺ and Mg²⁺ ions in hard water to form insoluble carbonates: Ca²⁺ + Na₂CO₃ → CaCO₃↓ + 2Na⁺. Similarly MgCO₃. These precipitates are removed, softening the water. Ion exchange uses zeolites or resins. Boiling removes only temporary hardness. Distillation is expensive.

Explanation:
Ant sting contains formic acid (methanoic acid, HCOOH), causing irritation. Nettle sting also contains formic acid. To neutralize, apply a base like baking soda. Acetic acid is in vinegar, citric acid in citrus fruits, lactic acid in sour milk and muscles. Formic acid is the simplest carboxylic acid.

Explanation:
Enzymes exhibit substrate specificity, meaning each enzyme catalyzes a particular reaction or acts on a specific substrate (lock-and-key model). For example, urease acts only on urea. This specificity is due to the unique shape of the active site. Denaturation is loss of structure, inhibition is blocking activity, optimum temperature is condition for maximum activity.