What is the blood resistivity if a 9.0 v potential difference causes a 210 μa current through the blood in the vein?

= 42,857.14 ohms.

According to ohm's Law; the current through a conductor is directly proportional to the potential difference at a constant temperature.

Therefore; V  I, thus; V = IR , Where R is the resistance.

Hence; Resistance, R = V/I

In this case;

Resistivity of column of blood = E/I

                                                  = 9/.00021,

                                                 = 42,857.14 ohms.  

come closer and become far apart and become steam/gas

wavelength divides in half and speed stays the same.