Which of the following reacts with benzene in the presence of anhydrous aluminum chloride to form acetophenone?

The quantum number which explains the line spectra observed as doublets in the case of hydrogen and alkali metals and doublets and triplets in the case of alkaline earth metals is

$A$ common-emitter amplifier is designed with a $n-p-n$ transistor $(\alpha = 0.99)$. The input impedance is $1 \, k\Omega$ and the load resistance is $10 \, k\Omega$. The voltage gain will be

Among the following,the compound that is both paramagnetic and coloured is

The atomic numbers of elements $A$,$B$,$C$ and $D$ are $Z-1$,$Z$,$Z+1$ and $Z+2$,respectively. If $B$ is a noble gas,choose the correct statements from the following:
$(1)$ $A$ has high electron affinity
$(2)$ $C$ exists in $+2$ oxidation state
$(3)$ $D$ is an alkaline earth metal

Lungs do not collapse between breaths and some air always remains in the lungs which can never be expelled because