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A crosscurrent cascade of N ideal stages is used to treat a feed stream of molar flow rate E. The feed stream contains a solute which is to be recovered by a pure solvent having a molar flow rate S. The solvent is divided equally between these N stages. The linear equilibrium curve relating the mole fraction x and y* of the solute in the raffinate and the extract respectively, is given by y* = mx. Assume dilute conditions.The ratio of the solute mole fraction in the original feed to that in the exit raffinate stream i.e. (x${_0}/x{_N}$) is given by

- [1+($\frac {mS}{NE}$)]$^{N}$
- [1+($\frac {NS}{mE}$)]$^{N}$
- [1+($\frac {NE}{mS}$)]$^{N}$
- [1+($\frac {mE}{NS}$)]$^{N}$