
Explanation:
Natural length of a spring is
. The spring is streched by
. The resultant energy of the spring is
.
The potential energy of an ideal spring with spring constant
and elongation
is given by
.
So, in the current problem, the natural length of the spring is not required to find the spring constant
.

∴ The spring constant of the spring = 
The moment of a couple is Force × perpendicular distance from the arm of the line of action
so the arm of the couple= moment of couple/force=8.5/34=0.25m
the arm is 0.25m
Answer:
Conductivity probe
Explanation:
The Conductivity Probe consists of two electrodes(also referred to as probes)or an electrode and a wall vessel where the material in the vessel completes the circuit as the level rises in the vessel.
It is used in measuring solution conductivity or total ionic concentration of aqueous samples.
I believe it’s A. I know for sure it isn’t D.