Pick out the wrong statement.

• The vessel dispersion number (D/UL) for plug flow and mixed flow approaches zero and infinity respectively.
• Space time in a flow reactor is a measure of its capacity and is equal to the residence time when the density of reaction mixture is constant.
• Mixed reactor is always smaller than the plug flow reactor for all positive reaction orders for a particular duty.
• In an ideal tubular flow reactor, mixing takes place in radial direction and there is no mixing in logitudinal direction.