Answer:

Explanation:
According to the law of conservation of linear momentum, the total momentum of both pucks won't be changed regardless of their interaction if no external forces are acting on the system.
Being
and
the masses of pucks a and b respectively, the initial momentum of the system is

Since b is initially at rest

After the collision and being
and
the respective velocities, the total momentum is

Both momentums are equal, thus
Solving for 


The initial kinetic energy can be found as (provided puck b is at rest)


The final kinetic energy is


The change of kinetic energy is

Data Analysis and Conclusion
The molecular geometry of both F2 and HF is linear.There are only two atoms which are covalently bonded and thus, the bonding scheme with the atoms looks like this;
F --- F
H---F
So, both are linear.
Im not sure but it might be the last option: it gives reasons to be believed and trusted