Which metal is used in the thermite process for welding railway tracks? MCQ with Answer and Explanation

Explanation:
In PCl₅, phosphorus forms five covalent bonds with five chlorine atoms. Phosphorus has 5 valence electrons (3s²3p³), and by using d-orbitals, it can expand its octet to accommodate 5 bonds. Thus its covalency is 5. In PCl₃, it is 3. Valency is the number of bonds formed. The oxidation state of P in PCl₅ is +5.

Explanation:
Baking powder contains sodium bicarbonate (NaHCO₃) and a weak solid acid such as tartaric acid or cream of tartar (potassium hydrogen tartrate). When moistened, they react to produce CO₂, making dough rise. Baking soda alone requires an acidic ingredient (yogurt, lemon). The acid in baking powder ensures reliable leavening. Sodium chloride and calcium carbonate do not serve this purpose.

Explanation:
Neutralization is the reaction of an acid with a base to produce salt and water. However, the resulting solution is not always neutral (pH 7) because the salt may undergo hydrolysis. If the acid is strong and base weak (e.g., HCl + NH₄OH), the salt (NH₄Cl) is acidic, pH < 7. If acid is weak and base strong (CH₃COOH + NaOH), salt is basic, pH > 7. Only strong acid-strong base gives pH 7.