Chemical Reactions and Equations

Hydrogen; because water has two hydrogen atoms for every one oxygen atom

Step 1: The balanced equation for electrolysis of water is: 2H₂O → 2H₂ + O₂. Step 2: From this equation, 2 moles of H₂ are produced for every 1 mole of O₂. So the volume ratio of H₂ : O₂ = 2 : 1. Step 3: The cathode is the negative electrode where reduction occurs — H⁺ ions gain electrons to form H₂ gas. Step 4: The reason for double volume is purely due to the molecular formula of water (H₂O) — 2 hydrogen atoms per 1 oxygen atom, giving twice as many H₂ molecules. Step 5: Option A is wrong — cathode produces hydrogen, not oxygen. Option C gives the right substance but the WRONG reason — the v

Ba²⁺ and SO₄²⁻ form BaSO₄ precipitate; double displacement (precipitation) reaction

Step 1: In this reaction, two ionic compounds (Na₂SO₄ and BaCl₂) react by exchanging their ions — this is a double displacement reaction. Step 2: Na⁺ pairs with Cl⁻ to form NaCl (soluble, stays in solution) and Ba²⁺ pairs with SO₄²⁻ to form BaSO₄ (insoluble, forms a white precipitate). Step 3: BaSO₄ is the white precipitate because it is insoluble in water. NaCl is soluble and remains dissolved. Step 4: Since a precipitate is formed, this is also called a precipitation reaction. Step 5: All other options incorrectly identify the ions forming the precipitate or the reaction type. NaCl is always

Nitrogen prevents oxidation (rancidity) of chips; nitrogen is an inert/unreactive gas

Step 1: Chips contain fats and oils. When fats/oils react with oxygen in air, they get oxidised and become rancid — this means their taste and smell change unpleasantly. Step 2: To prevent this oxidation (rancidity), chips manufacturers remove oxygen from the packet by replacing it with nitrogen gas. Step 3: Nitrogen is used because it is chemically inert — it does not react with fats, oils, or the food itself, so it doesn't affect taste or quality. Step 4: The nitrogen acts as a 'shield' by eliminating the oxygen that would cause oxidation. Step 5: Option A is wrong — nitrogen doesn't prevent

A combination reaction and also an oxidation reaction (Mg is oxidised)

Step 1: Two substances (Mg and O₂) combine to form one single product (MgO) — this is the definition of a combination reaction. Step 2: Magnesium (Mg) gains oxygen to form MgO — gaining oxygen means it is OXIDISED. So this is also an oxidation reaction. Step 3: Heat and brilliant white light are released during this reaction, making it exothermic. Step 4: This reaction has two labels: combination + oxidation. Both are correct simultaneously. Step 5: Option A is wrong — decomposition reactions break ONE compound into multiple products, which is the opposite. Option C is wrong — no element repla