I would have to say that it is Y
The initial volume of the gas is

while its final volume is

so its variation of volume is

The pressure is constant, and it is

Therefore the work done by the gas is

where the negative sign means the work is done by the surrounding on the gas.
The heat energy given to the gas is

And the change in internal energy of the gas can be found by using the first law of thermodynamics:

where the positive sign means the internal energy of the gas has increased.
As velocities are tangent, the value of both Particle A and Particle B would be same for that point O (Intersecting point)
a = v / t
Here, v = 7, t = 6
So, a = 7/6
a = 1.17
As the graph is decreasing, value of acceleration would be negative.
So, a = -1.17 m/s²
In short, Your Answer would be Option C
Hope this helps!