Live practice

An isolated system exchanges neither matter nor energy. The second law requires its entropy to increase in a spontaneous irreversible process and remain constant only at equilibrium/reversible limit.

The magnitude and direction of molecular dipole moment reveal bond polarity and whether bond moments cancel. It helps distinguish geometrical isomers, infer molecular shape and estimate ionic character.

B loses a higher-energy, less-penetrating 2p electron, whereas Be would lose from filled 2s. N has the stable half-filled 2p³ arrangement; O has one paired 2p electron, so repulsion makes removal easier.

Use En=E₁/n² and rn=n²a₀ with a₀=52.9 pm.

A reported measurement contains digits known with certainty followed by one estimated digit. Together they express the precision of the measurement.

Principle and reasoning. Work from the governing physical relation and apply it to every stated part.

Use conservation of volume flow rate.

Principle and reasoning. Work from the governing physical relation and apply it to every stated part.

Use the definition of bulk modulus; the litre value cancels in the fractional change.

Inside a uniform Earth, g is proportional to the distance from the centre. Halfway down means r=\(\frac{R}{2}\).

Write Newton's second-law equation for each mass, taking the \(12\,\mathrm{kg}\) mass downward as positive.

Take moments about the new balance point at \(45.0\,\mathrm{cm}\).