Odisha BSE HSC General Science common mistakes
Odisha BSE HSC General Science · Understand the traps and how to avoid them.
In mirror and lens numericals, substituting object distance, image distance and focal length with all positive values, or guessing signs from the diagram instead of applying the Cartesian sign convention.
Students memorise the mirror/lens formula but practise only with positive numbers; the question stem often gives object distance as a positive value, so they plug it in unchanged and lose the sign mark.
What to do instead
Before substituting, write the sign-convention table, mark the direction of incident light on a quick ray sketch, then substitute with signs and check that a virtual image gives a positive image distance.
Writing chemical equations without balancing them or without state symbols and conditions, for example Fe + H2O gives Fe3O4 + H2 or Zn + HCl gives ZnCl2 + H2.
Candidates treat the equation as a word equation copied from the textbook and do not count atoms; the marking scheme awards separate marks for correct formulae, balancing, states and conditions.
What to do instead
Use a five-step checklist: correct formulae, balance each element, add (s), (l), (g) or (aq), add heat, steam or catalyst, and re-count oxygen and hydrogen last.
In differentiate-between questions, writing two separate paragraphs describing artery and vein instead of a point-by-point table on the basis asked, such as wall thickness, valves and direction of blood flow.
Students revise definitions but not the comparison format, and they lose time writing long sentences that do not earn the comparison marks.
What to do instead
Prepare three-column tables for common pairs such as artery and vein, mitosis and meiosis, and xylem and phloem, with the basis in column one and one short phrase per side; draw the table even when the question does not explicitly demand it.
Answering pollution-control questions with generic slogans such as reduce, reuse, recycle or plant trees instead of naming a specific cause, effect and control measure for the pollutant asked.
Textbook chapters are abstract and candidates have not linked them to local examples; two-mark questions reward precise terms such as fly ash, effluent and particulate matter.
What to do instead
For each major pollutant such as fly ash, plastic, industrial effluent, vehicular emission and pesticide, memorise a three-line card: source, health or environmental effect, and one engineering or behavioural control; quote one Odisha example where possible.
Confusing valency when writing formulae, for example writing CaCl, NaSO4, AlO or MgOH instead of CaCl2, Na2SO4, Al2O3 and Mg(OH)2.
Candidates memorise compound names as strings and do not use the criss-cross method or check charge neutrality, so one mark is lost before any calculation begins.
What to do instead
Write the ions with charges above the symbols, criss-cross the numerical valencies, drop the number one, and check that total positive charge equals total negative charge; bracket polyatomic ions such as OH minus and SO4 2 minus.
In electricity numericals, adding resistances as if all were in series when the circuit shows a parallel branch, or writing the reciprocal formula but forgetting to invert the result at the end.
The formula is memorised without a node-identification step, and the circuit diagram in the question paper is small and easy to misread under time pressure.
What to do instead
Redraw the circuit with coloured nodes, label each resistor as series or parallel, calculate the parallel block first, invert last, and sanity-check that the equivalent resistance of a parallel combination is smaller than the smallest branch.
Drawing diagrams such as the human digestive system, nephron, flower or reflex arc without labels, with label lines crossing, or labelling parts not asked; sometimes using ink and double lines.
Diagrams are treated as decoration at the end of an answer, and candidates run out of time and skip labels even though labelled diagrams carry specific marks.
What to do instead
Use a sharp pencil, single clear lines, horizontal labels without arrowheads and a title; practise a five-label minimum for each prescribed diagram and label exactly the parts named in the question.
In practical-based questions, naming the gas correctly but not giving its test, or writing that carbon dioxide turns limewater milky when the gas is oxygen; omitting observations for acids, bases and salts.
Practical work is often hurried before the board exam, and observation tables are memorised without being linked to the corresponding equation or conclusion.
What to do instead
Learn a ten-row gas and ion test table with the exact observation, for example carbon dioxide turns limewater milky and the milkiness disappears with excess gas, hydrogen burns with a pop, and oxygen relights a glowing splint; write the observation before the conclusion.
Leaving final numerical answers without units or mixing units such as centimetre and metre, gram and kilogram, or milliampere and ampere after substitution.
Students focus on the number and rush the last line, while the question stem may give non-SI units that must be converted before using the formula.
What to do instead
Convert all given quantities to SI in the given line, carry units through the calculation, write the answer as a number with its unit and direction where needed, and underline the final answer.
Drawing food chains and food webs with arrows pointing from predator to prey, or leaving trophic levels unlabelled and confusing producers with decomposers.
The arrow is read as eaten by rather than energy flows to, and examples are learnt without the trophic-level vocabulary needed for the explanation mark.
What to do instead
Always draw the arrow from the organism being eaten to the eater, label T1, T2 and T3 or producer, primary consumer and secondary consumer, and practise a local four-step chain such as paddy to grasshopper to frog to snake.