Flow of a liquid is most streamlined (least turbulent) when:

Liquid of high viscosity and high density flows through a tube of small radius
Liquid of high viscosity and low density flows through a tube of small radius
Liquid of low viscosity and low density flows through a tube of large radius
Liquid of low viscosity and high density flows through a tube of large radius

Correct answer: Liquid of high viscosity and low density flows through a tube of small radius

Solution

Reynolds number Re = rho*v*d/eta. Flow is most streamlined when Re is smallest, i.e. high viscosity (eta large), low density (rho small), and small radius (d small). This matches option 2.

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