CBSE Science evaluations follow strict NCERT keyword rubrics. Explaining a concept accurately in your own words while missing the official NCERT terminology often receives zero marks.
1. Light: Sign Convention Heuristic
The New Cartesian Sign Convention: Object distance ($u$) is always negative. Real inverted images have negative magnification ($m < 0$); virtual erect images have positive magnification ($m > 0$). Convex mirrors and convex lenses always have positive focal lengths ($f > 0$).
2. Chemistry: Reactivity Series and Redox
Displacement reactions, rusting prevention, and chlor-alkali process reactions ($2NaCl + 2H_2O \rightarrow 2NaOH + Cl_2 + H_2$) must be accompanied by state symbols and gas release identification.
