What is used to represent the $C=C$ bond in a ball and stick model?

What is a multiple bond? Give the difference between a single bond,a double bond,and a triple bond.

The electronic configuration of $X$ and $Y$ are given below:
$X: 1s^2 2s^2 2p^6 3s^2 3p^3$
$Y: 1s^2 2s^2 2p^6 3s^2 3p^5$
Which of the following is the correct molecular formula and type of bond formed between $X$ and $Y$?

Which of the following forces hold the carbon atoms together in diamond?

Which of the following is the strongest bond?

Which of the following bonds has the highest bond enthalpy?