TN State Board 10th Science Question Paper 2025

1 kilogram-force (kgf) is the force exerted by gravity on a mass of 1 kg. Since $1\,\text{kgf} = 9.8\,\text{N}$ and $1\,\text{N} = 10^5\,\text{dyne}$, we get $1\,\text{kgf} = 9.8 \times 10^5\,\text{dyne} = 98 \times 10^4\,\text{dyne}$. Hence, option (c) is correct. The other options do not match the standard conversion.

Presbyopia is an age-related defect of vision in which the power of accommodation of the eye decreases. It is usually corrected by using a bifocal lens, which has both convex and concave portions to help in near and distant vision. Hence, option (d) is correct. Convex and concave single lenses are used for specific defects like hypermetropia and myopia, respectively, while a convex mirror is not used for correcting eye defects.

Potential difference is given by $V = \frac{W}{Q}$. Here, work done $W = 100\,\text{J}$ and charge $Q = 10\,\text{C}$. So, $V = \frac{100}{10} = 10\,\text{V}$. Therefore, option (b) is correct.

Artificial radioactivity was discovered by Irene Curie and Frédéric Joliot. Among the given options, Irene Curie is correct. Becquerel discovered natural radioactivity, Roentgen discovered X-rays, and Neils Bohr is known for the atomic model.

Mercury ($\text{Hg}$) is an important metal used to form amalgams, which are alloys of mercury with other metals. Hence, option (b) is correct. Silver, magnesium, and aluminium are not the metal used to form amalgam in this context.