What causes the formation of beats in sounds?

$A$ set of $14$ tuning forks is arranged in a series of increasing frequencies. Each fork produces '$x$' beats per second with the preceding fork and the last fork is an octave of the first fork. If the seventh fork has the frequency of $114 \text{ Hz}$, the value of $x$ is

Two tuning forks $A$ and $B$ produce $4$ beats per second. The frequency of $A$ is $256 \ Hz$. On loading $B$ slightly,the beat frequency becomes $5$ beats in $2$ seconds. The frequency of $B$ after loading is .... $Hz$

Two tuning forks have frequencies $450\, Hz$ and $454\, Hz$ respectively. On sounding these forks together,the time interval between successive maximum intensities will be .... $sec$

The intensity of a sound appears to an observer to be periodic. Which of the following can be the cause of it?

$A$ tuning fork sounded together with a tuning fork of frequency $256 \ Hz$ emits $2$ beats per second. On loading the tuning fork of frequency $256 \ Hz,$ the number of beats heard is $1$ per second. The frequency of the unknown tuning fork is: (in $Hz$)