Live practice

The universal set must contain \(A\cup B\cup C=\{0,1,2,3,4,5,6,8\}\). Only option (iii) contains all these elements; (i) lacks 8, (ii) has none, and (iv) lacks 0.

(i) Right-hand thumb rule: thumb points with current; curled fingers give field. (ii) Fleming's left-hand rule: first finger field, second finger current, thumb force, mutually perpendicular. (iii) Fleming's right-hand rule: first finger field, thumb conductor motion, second finger induced current.

Electrical energy converted to heat is \(H=VQ\).

A magnifier must be a convex lens with the object inside its focal length. Greater power, hence shorter focal length, produces larger angular magnification. The \(5\,\mathrm{cm}\) convex lens is best.

• Barrier: condoms/diaphragms prevent sperm reaching the ovum; condoms also reduce STIs.
• Hormonal: pills, injections or implants inhibit ovulation and alter cervical/uterine conditions.
• Intrauterine devices: copper-T impairs sperm and prevents fertilisation.
• Surgical: vasectomy cuts vas deferens; tubectomy blocks fallopian tubes.
• Natural methods: fertility awareness or abstinence during fertile days, though less reliable.

The shoot tip detects light. Auxin redistributes to the shaded side, where it promotes greater cell elongation than on the illuminated side. Unequal growth curves the shoot towards light. Removing the tip or blocking it from light prevents this phototropic curvature.

• Oxygen, carbon dioxide and water vapour diffuse through stomata and lenticels.
• Excess water is removed by transpiration or guttation.
• Wastes are stored in vacuoles, old leaves, bark, fruits or old xylem and removed when parts fall.
• Some wastes are converted into resins, gums, latex or crystals.
• Some substances are released into surrounding soil through roots.

Ethanoic acid has a sour, vinegar-like smell and turns blue litmus red; ethanol is neutral to litmus and has a characteristic alcoholic smell. Ethanoic acid reacts with sodium hydrogencarbonate to release \(\ce{CO2}\):

Ethanol shows no effervescence. Their boiling points also differ: ethanol about 78 °C and ethanoic acid about 118 °C.

Hammer test: strike each sample gently. A metal is usually malleable and flattens; a solid non-metal is generally brittle and breaks.

Conductivity test: insert the sample into a complete battery-bulb circuit. A glowing bulb indicates electrical conduction, characteristic of metals.

These tests are not absolute. Graphite is a non-metal that conducts electricity; zinc can be brittle at room temperature, and some non-metals are soft. Conclusions should therefore use several properties together.

Turning red litmus blue identifies a base. A basic solution has pH above 7. Among the values 1, 4, 5 and 10, only 10 is above 7.