The reaction of acetaldehyde with conc. $KMnO_4$ gives

Which of the following compounds gives a positive test with $2,4$-$DNP$ ($2$,$4$-dinitrophenylhydrazine)?
$(a)$ Acetone
$(b)$ Butan-$2$-one
$(c)$ Acetaldehyde
$(d)$ Formaldehyde

What is the name of the reaction when $C_6H_5CHO$ (benzaldehyde) changes into $C_6H_5CH_2OH$ (benzyl alcohol)?

Arrange the following compounds in the increasing order of their equilibrium constants for the formation of a hydrate:
$(I)$ $6$-amino-$1$-tetralone
$(II)$ $7$-amino-$1$-tetralone
$(III)$ $1$-tetralone
$(IV)$ $6$-nitro-$1$-tetralone

The end product $(C)$ in the following reaction is:

Which of the following gives the iodoform test?