Live practice

Zero electronegativity difference makes N₂ non-polar. Differences rise from Cl–F to S–O and then to the metal–non-metal compounds; Li–F has the largest difference.

Al falls as expected because its valence shell is farther out. Poor shielding by filled 3d electrons raises Ga slightly. Poor shielding by 4f and 5d electrons and relativistic/inert-pair effects raise Tl.

Ionisation takes the electron from E₂ to zero; the threshold wavelength follows from E=hc/λ.

Leading zeros are not significant; zeros between non-zero digits are significant; trailing zeros without a decimal point are normally not taken as significant; trailing zeros after a decimal point are significant.

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

A liquid drop has one surface, so its excess pressure is 2S/r.

A circular satellite has total energy −GMm/(2r). The least escape energy raises this total to zero.

The leaking sand has the same horizontal velocity as the trolley at separation, so it exerts no horizontal thrust. With no external horizontal force, the trolley speed stays unchanged.

The system starts at rest, so total linear momentum remains zero.

Use the sequence definition or geometric-progression formula, keeping the first-term offset explicit.

The displayed substitutions cover every requested part and verify the result against the original data.

The word contains eight distinct letters.