Haryana BSEH Secondary Science common mistakes
Haryana BSEH Secondary Science · Understand the traps and how to avoid them.
While balancing a chemical equation, candidates change the subscripts inside a formula (writing H2O2 as H2O to make atoms match) instead of placing coefficients in front of the formulas.
Balancing is taught as 'making the numbers equal on both sides', and students treat the small subscript digits as adjustable counters. They have not internalised that a subscript defines the identity of the substance, so altering it produces a different compound entirely.
What to do instead
Drill the rule 'coefficients only, never subscripts' by having the candidate write the full atom tally under each formula, then add coefficients and re-tally. Practise with H2 + O2 -> H2O and Fe + O2 -> Fe2O3, and after each attempt ask: 'Is every formula still the same substance I started with?'
Candidates write word equations or observations for reactions that do not occur (e.g. 'copper + dilute hydrochloric acid gives hydrogen') or predict a displacement reaction between two metals where the solid metal is less reactive than the one in solution.
Students memorise isolated 'metal + acid gives hydrogen' statements without attaching the condition of reactivity, and they do not hold a reliable reactivity series in memory, so they apply the pattern indiscriminately.
What to do instead
Have the candidate build the reactivity series from memory daily (K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Hg, Ag, Au) and apply two check questions before predicting any product: 'Is the metal above hydrogen?' for acids, and 'Is the free metal more reactive than the one in the salt?' for displacement. Test the negative cases explicitly, e.g. Cu + dilute HCl and Ag + CuSO4.
When explaining why a person with a defect in a specific organ or hormone shows particular symptoms, candidates name the gland or organ but give no causal chain, or they confuse the role of insulin, thyroxine, and adrenaline in the answer.
Control and coordination is studied as a list of glands and hormones rather than as feedback systems, so students can recall names but cannot reason from a symptom back to a cause, which is what the question actually tests.
What to do instead
For each hormone, write a three-line causal chain: source gland, target organ, effect of excess and of deficiency. For example: pancreas, insulin, lowers blood glucose; deficiency causes glucose in urine and thirst. Then practise reverse questions ('a patient is always thirsty and passes sugary urine; which hormone and which gland?').
Candidates label the direction of reflected or refracted rays incorrectly: they draw the normal on the same side as the incident ray, or place the image on the same side of a plane mirror as the object.
Students copy ray diagrams as pictures without constructing them from the laws, so the geometric relationship between incident ray, normal, and reflected ray is not anchored, and mirror conventions are easily reversed under exam pressure.
What to do instead
Require every diagram to start with the normal drawn first, then the incident ray, with the angle marked between the ray and the normal (not the surface). Use a ruler and protractor on at least ten practice diagrams, and for plane mirrors state in words: image is behind the mirror, same distance as the object, virtual and laterally inverted.
In numerical problems on Ohm's law and series/parallel circuits, candidates add resistances in the wrong combination, or apply the full supply voltage across a single resistor in a series circuit.
The formulas R = R1 + R2 and 1/R = 1/R1 + 1/R2 are memorised as text without a mental model of current and potential difference, so students cannot check whether their combination makes physical sense.
What to do instead
Before calculating, draw the circuit and mark where current splits (parallel) and where it is the same (series). Teach the sanity check: equivalent resistance of a parallel combination must be smaller than the smallest branch, and of a series combination larger than the largest. Solve one problem each way daily and verify with the check before submission.
Candidates confuse the heating effect and magnetic effect of current, or state that a fuse and an earth wire perform the same protective function.
The applications are studied as separate facts (bulb, electromagnet, fuse, earthing) rather than linked to the underlying effect, so in application questions the student picks whichever term sounds familiar.
What to do instead
Make a two-column table: effect of current, principle, and appliance. Under heating put filament bulb, fuse, electric iron; under magnetic put electromagnet, electric bell, motor. Then write one sentence each on how a fuse breaks the circuit on overload whereas earthing provides a low-resistance path to divert leakage current.
On environment questions, candidates give a single cause for a phenomenon (e.g. 'global warming is caused by pollution') without naming the specific gas, process, or consequence asked for, and they mix up ozone depletion with the greenhouse effect.
Environment topics are revised as slogans and awareness phrases rather than as cause-effect science, so answers stay at the level of generalities that earn little credit.
What to do instead
For each issue build a cause-mechanism-consequence-remedy card. For example: CFCs, chlorine breaks ozone in the stratosphere, more UV reaches the ground, phase out CFCs. For the greenhouse effect: CO2 and methane trap infrared radiation, average temperature rises, sea level and crop patterns change. Keep the two cards physically separate so the mechanisms are not merged.
In practical questions, candidates describe the aim or the apparatus but omit the observation table, the controlled variable, or the precaution that explains an anomalous reading.
Practical work is often learned as a procedure to be recited, and students do not realise that examiners award marks for variables, observations, and error control rather than for naming glassware.
What to do instead
Answer every practical question in a fixed four-part frame: aim, variables (what is changed, what is measured, what is kept constant), observation with units, and one precaution linked to the likely error. Rehearse with familiar experiments such as verifying Ohm's law, testing starch with iodine, and finding the focal length of a concave mirror.
Candidates use everyday meanings of scientific words in answers, writing 'the plant breathes' or 'the current is used up as it goes round the circuit', instead of the technical term required.
School science teaching uses everyday language alongside technical terms, and students do not distinguish between the two registers, so their answers read as colloquial and lose precision marks.
What to do instead
Keep a personal substitution list: 'breathes' becomes 'respires' or 'gaseous exchange occurs'; 'used up' becomes 'energy is transferred and charge is conserved'. After each practice answer, underline any word that would not appear in the textbook and replace it with the exact term.
On health and nutrition questions, candidates treat a deficiency disease as caused by a germ, or recommend a food without naming the nutrient it supplies (e.g. 'eat green vegetables' with no mention of iron or vitamin A).
Deficiency diseases and infectious diseases are revised in the same chapter-cluster and the distinction between a missing nutrient and a pathogen is not made explicit, so the causal agent is guessed.
What to do instead
Pair every disease with its cause type and its corrective food: anaemia, iron deficiency, green leafy vegetables; night blindness, vitamin A, carrots and papaya; goitre, iodine, iodised salt; kwashiorkor, protein, pulses and milk. Contrast each with one infectious disease such as tuberculosis, caused by a bacterium, to keep the categories distinct.