The answer is either
b A system in which Newton's Laws are valid
or
c A system in which there are no external forces.
Explanation:
not a, and not d
There are energy changes in a closed system.
A closed system obeys the conservation laws in its physical description.
I am thinking that maybe the problem is not with the calibration. It might be that the buffered solution is already expired since at this point the solution is already not stable and will give a different pH reading than what is expected.
Answer:
The magnitude of electron acceleration is

Explanation:
Given:
Distance from the wire to the field point
m
Speed of electron 
Current
A
For finding the acceleration,
First find the magnetic field due to wire,

Where 

T
The magnetic force exerted on the electron passing through straight wire,

N
From the newton's second law

Where
mass of electron
kg
So acceleration is given by,



Therefore, the magnitude of electron acceleration is

Answer:
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Explanation: