In wastewater treatment plants, the shape of the particle directly affects the settling velocity of the particle during sedimentation. For an irregular shaped particle like a disc, it is normally a challenge to estimate the settling; thus, the equivalent sphere diameters are used in place of the apparent diameter of the particle. For a disc$-$shaped particle of diameter $3\mathrm{.}00$ mm and thickness $0\mathrm{.}500$ mm$,$ estimate the$1\mathrm{.}3\mathrm{.}1\mathrm{.}2\mathrm{.}1.$ Equivalent volume sphere diameter. $1\mathrm{.}2\mathrm{.}2.$ Equivalent surface sphere diameter. $1\mathrm{.}2\mathrm{.}3.$ Surface$-$volume diameter$\mathrm{.}1\mathrm{.}2\mathrm{.}4.$ Sphericity$1\mathrm{.}2\mathrm{.}5.$ Sieve diameter