How does the size of an atom relate to its electronegativity?

Electronegativity is a relative measure of the force of attraction between an atom and the electrons it is sharing in a bond with another atom. It decreases as one goes down a group because as the atomic radius increases, there is less attraction between the nucleus and shared electrons (Coulomb's Law).

Wavelength divides in half and speed stays the same.

Since you have not included the experiment situation and the data, of course, i can not give you specific details about it. but i can you with this question.1) i will assume that the motion is projectile (parabolic) motion.2) yes, the horizontal distance depends on the horizontal velocity as, naming vx the horizontal velocity and t the time, it is: x = vx × t3) now, observe that the flight time depends on the vertical velocity as, naming voy the initial vertical velocity, t the time and y the vertical distance before reaching the ground: y = yo + voy×t - gt² / 2.the higher the initial vertical velocity (voy) the longer the object will be flying and so t will be higher in the equation for the horizontal distance.that explains the relationship between the horizontal distance and the horizontal velocity.