Is viscosity a vector or a scalar?

$A$ river $10\,m$ deep is flowing at $5\,m/s$. The shearing stress between horizontal layers of the river is :- $(\eta = 10^{-3}\,SI\,unit)$

Define the coefficient of viscosity.

Define velocity gradient and give its unit. Also,write the dimensional formula of the velocity gradient.

$A$ cylindrical metal box whose flat surface has an area of $0.01 \ m^2$ rests on a liquid layer of $0.3 \ mm$ thickness. If upon applying a horizontal force of magnitude $\frac{1}{3} \ N$,the box slides with a constant speed of $0.09 \ m/s$,the coefficient of viscosity of the liquid is nearly:

Write one practical use of viscosity.