What is the use of this jet aircraft with tanks between biplane wings?
It is the Polish PZL M-15, as you can read in the image if you zoom in. From Wikipedia: 


  The aircraft was designed in Poland in response to a Soviet
  requirement for a new agricultural plane.


Agricultural airplanes fly slow and having a shorter span increases the number of (air)fields you can land on. That's probably why they decided using a biplane design.  

The two tanks outside the fuselage could have several reasons:


Placing the chemicals further away from the turbine and pilot
Reduce the bending moment at the wing root
Shorter pipes between the tank and the spray nozzles


All this, of course, at the cost of a lot of drag. As explained in the image source page, fuel consumption was three times larger than other agricultural airplanes and it had a really bad maneuverability.

The jet engine was a requirement dictated by Aeroflot, who wanted to use the same type of fuel for their passenger and agricultural airplanes.