Live practice

Touch-me-not movement is rapid, non-directional and independent of growth. Touch causes electrical/chemical signals and changes in water content and turgor of motor cells. Phototropism is a slow, directional growth response; unequal auxin distribution makes cells on the shaded side elongate more, bending the shoot towards light.

Hydrochloric acid creates the acidic pH required to convert pepsinogen to active pepsin and for pepsin to digest proteins. It also kills many microorganisms entering with food. The stomach mucus protects the lining from this acid.

(i) Two-carbon haloalkane: bromoethane. (ii) One-carbon aldehyde: methanal. (iii) Six-carbon chain numbered from the triple-bond end, with the triple bond starting at carbon 1: hex-1-yne.

Zinc is above iron in the reactivity series, so it displaces iron from iron(II) sulphate:

The pale-green colour of iron(II) sulphate fades because zinc sulphate is colourless, and grey iron is deposited on the zinc.

Acidic behaviour requires hydrogen chloride to dissolve in water and form hydronium ions:

Dry litmus supplies no water, so dry HCl does not ionise. In the absence of hydronium ions, the indicator does not change colour.

Principle. The ideal-gas law fixes N=PV/(kT), while vrms=√(3RT/M).

Their molar masses differ, so their rms speeds differ. Neon has the smallest molar mass and therefore the largest rms speed; UF₆ has the smallest.

Principle. Work is signed area under the P–V path. The linear expansion uses average pressure; the isobaric compression has negative ΔV.

Principle. Tensile strain equals stress divided by Young modulus.

Principle. For an isolated pair, momentum is conserved at every instant. During contact, translational kinetic energy can be stored temporarily as elastic potential energy.

Principle. During every free-flight segment speed changes linearly with slope magnitude g; impact causes an instantaneous downward jump in speed magnitude.