What are closed pipe and open pipe?

If the length of a closed organ pipe is $1 \ m$ and the velocity of sound is $330 \ m/s$,then the frequency for the second note (first overtone) is:

$A$ tuning fork produces four beats per second with two open organ pipes having lengths $30 \ cm$ and $31 \ cm$. Find the frequency of the tuning fork in $Hz$.

$A$ pipe open at both ends and a pipe closed at one end have the same length and both are vibrating in their fundamental mode. If the air column vibrating in the open pipe has a resonance frequency $n_1$ and the air column vibrating in the closed pipe has a resonance frequency $n_2$,then:

Two pipes of lengths $L_1$ and $L_2$,open at both ends,are joined in series. If $f_1$ and $f_2$ are the fundamental frequencies of the two pipes,then the fundamental frequency of the series combination will be (neglect end correction).

In a resonance tube experiment,when the tube is filled with water up to a height of $17.0 \, cm$ from the bottom,it resonates with a given tuning fork. When the water level is raised,the next resonance with the same tuning fork occurs at a height of $24.5 \, cm$. If the velocity of sound in air is $330 \, m/s$,the tuning fork frequency is $...... \, Hz$.