The correct answer is: A. The pressure intensity at vena contracta is atmospheric.
Vena contracta is the minimum cross-sectional area of a fluid jet in a converging-diverging nozzle. The pressure at vena contracta is always less than atmospheric pressure. This is because the fluid accelerates as it flows through the nozzle, and the acceleration of a fluid is accompanied by a decrease in pressure.
The coefficient of contraction is a dimensionless number that is used to characterize the contraction of a fluid jet. It is defined as the ratio of the minimum cross-sectional area of the jet (at vena contracta) to the cross-sectional area of the nozzle at the throat. The coefficient of contraction is always less than one, and its value depends on the shape of the nozzle.
Streamlines are lines that are tangent to the velocity vectors of a fluid. In a converging-diverging nozzle, the streamlines are parallel throughout the jet at vena contracta. This is because the velocity of the fluid is the highest at vena contracta, and the fluid particles are moving in straight lines.