Hello
Let's convert first the height from foot to meters:

This is the space covered by the ball in its accelerated motion, where the acceleration is the gravitational acceleration:

The law of motion is given by

Re-arranging, we can get the total time of the motion:

which is the time the ball takes to hit the ground.
Answer:
b. Both the gratings will produce the same separation of peaks.
e. The grating with 10 slits will produce better-defined(narrower) peaks.
Weight because both gravity and weight are pulling an object down
I can confirm it is not b.
Answer:
Ionic Compound
Explanation:
To identify the type of chemical bond in a molecule, look at the atoms that make up the compound. If there are two nonmetals, it is a covalent bond. If the two atoms are metals, it is a metallic bond. If one atom is a metal and the other is a nonmetal, it is an ionic bond. Ionic compounds are also known as salts. You can identify KBr as an ionic compound because potassium is a metal and a salt.
Hope this helps