SOF NSO cheat sheet

Reactivity series (decreasing): K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au; metals above H displace H2 from dilute acids, metals above Zn displace Zn from zinc salts.

Metals: malleable, ductile, sonorous, good conductors, form basic oxides; non-metals: brittle, poor conductors (except graphite), form acidic or neutral oxides.

Ionic bond forms by transfer of electrons (metal to non-metal); covalent bond forms by sharing (e.g., H2, O2, CH4, NH3); carbon shows catenation and tetravalency.

Homologous series members differ by CH2 (14 u); general formulas: alkanes CnH2n+2, alkenes CnH2n, alkynes CnH2n-2; alcohols CnH2n+1OH.

Ethanol oxidizes to ethanoic acid (CH3COOH); ethanoic acid + NaHCO3 gives brisk CO2 effervescence, distinguishing it from ethanol; esterification with alcohol gives sweet-smelling ester.

Ohm's law V = IR; series R = R1+R2+..., current same; parallel 1/R = 1/R1+1/R2+..., voltage same; power P = VI = I2R = V2/R; energy kWh = P(kW) x t(h).

Magnetic field: field lines run N to S outside a magnet, never intersect; right-hand thumb rule gives field direction around a current-carrying wire; field of a solenoid resembles a bar magnet.

Human reproduction: sperm (haploid, motile, from testis) + ovum (haploid, from ovary) fuse in fallopian tube; zygote implants in uterus; placenta exchanges nutrients; gestation ~9 months.

Control and coordination: neuron transmits electrical impulse; reflex arc = receptor, sensory neuron, spinal cord, motor neuron, effector; hormones are slow chemical messengers (e.g., insulin lowers blood glucose).

Letter position: A=1 to Z=26; opposite letter pairs sum to 27 (A-Z, B-Y, C-X, D-W...); reverse alphabet position = 27 minus forward position.

For series a, b, c, d, check differences d-c, c-b, b-a; constant difference = arithmetic, constant ratio = geometric, alternating differences = mixed pattern.

Coding-decoding: test shift (+n or -n), reversal, and position-sum rules against every given pair before committing to one rule.

Blood relations: draw a family tree with gender symbols; never assume gender from a name; 'only son of my mother' = the speaker himself (male).

Direction sense: use a compass sketch; net displacement uses Pythagoras when the final path is perpendicular to the first (e.g., 3 km N then 4 km E gives 5 km).

Syllogism: a conclusion follows only if true in every possible Venn arrangement; 'some A are B' does not imply 'some B are not A'.

Odd-one-out: group by shared property (all perfect squares, all multiples of 7, all prime); the item lacking the property for all members is the answer.

Number analogy a:b :: c:? - identify the exact operation on a (square, +3, digit sum) and apply the same operation to c, not a different one.

Ranking puzzles: total = (rank from left + rank from right) - 1 when both ranks refer to the same person.

Dilute acid + metal gives H2 (burns with pop sound); dilute acid + metal carbonate/bicarbonate gives CO2 (turns limewater milky) - use the gas to identify the compound class.

Displacement logic: a more reactive metal displaces a less reactive one from its salt solution; no reaction if the added metal is below the salt's metal in the series.

Circuit reasoning: adding resistors in parallel lowers total resistance and increases current; adding in series raises resistance and lowers current for a fixed voltage.

Fuse and heating: heat H = I2Rt; a higher-current appliance needs a thicker fuse wire; a short circuit raises current sharply and blows the fuse.

Electromagnet strength increases with more turns, larger current, and a soft-iron core; reversing current reverses polarity but keeps strength the same.

Carbon compounds: isomers share molecular formula but differ in structure (e.g., C4H10 as n-butane and isobutane); unsaturated hydrocarbons decolourize bromine water.

Reproduction logic: self-pollination needs one flower, cross-pollination needs a pollinator; asexual reproduction (budding, fragmentation, binary fission) produces genetically identical offspring.

Reflex vs voluntary action: reflex is fast and spinal-cord mediated; voluntary action involves the brain; hormone effects are slower but longer-lasting than nerve impulses.

Data interpretation: compute ratio, percentage change = (new - old)/old x 100, and read units carefully; a graph's slope gives rate, its area often gives total quantity.