Solution:
$\text{Hint: A disproportionation reaction is a type of redox reaction in which the same substance is simultaneously oxidized and reduced.}$
$\text{Let's analyze the oxidation numbers of the elements in each reaction:}$
$1.\ \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$
$\text{In } \text{CH}_4\text{, C is } -4\text{, H is } +1\text{.}$
$\text{In } \text{O}_2\text{, O is } 0\text{.}$
$\text{In } \text{CO}_2\text{, C is } +4\text{, O is } -2\text{.}$
$\text{In } \text{H}_2\text{O}\text{, H is } +1\text{, O is } -2\text{.}$
$\text{Carbon is oxidized (} -4 \rightarrow +4 \text{) and oxygen is reduced (} 0 \rightarrow -2 \text{). This is not a disproportionation reaction as two different elements undergo oxidation and reduction.}$
$2.\ \text{CH}_4 + 4\text{Cl}_2 \rightarrow \text{CCl}_4 + 4\text{HCl}$
$\text{In } \text{CH}_4\text{, C is } -4\text{, H is } +1\text{.}$
$\text{In } \text{Cl}_2\text{, Cl is } 0\text{.}$
$\text{In } \text{CCl}_4\text{, C is } +4\text{, Cl is } -1\text{.}$
$\text{In } \text{HCl}\text{, H is } +1\text{, Cl is } -1\text{.}$
$\text{Carbon is oxidized (} -4 \rightarrow +4 \text{) and chlorine is reduced (} 0 \rightarrow -1 \text{). This is not a disproportionation reaction.}$
$3.\ 2\text{F}_2 + 2\text{OH}^{-} \rightarrow 2\text{F}^{-} + \text{OF}_2 + \text{H}_2\text{O}$
$\text{In } \text{F}_2\text{, F is } 0\text{.}$
$\text{In } \text{OH}^{-}\text{, O is } -2\text{, H is } +1\text{.}$
$\text{In } \text{F}^{-}\text{, F is } -1\text{.}$
$\text{In } \text{OF}_2\text{, O is } +2\text{, F is } -1\text{.}$
$\text{In } \text{H}_2\text{O}\text{, H is } +1\text{, O is } -2\text{.}$
$\text{Fluorine is reduced (} 0 \rightarrow -1 \text{ in } \text{F}^{-} \text{) and oxygen is oxidized (} -2 \rightarrow +2 \text{ in } \text{OF}_2 \text{). This is not a disproportionation reaction for a single element.}$
$4.\ 2\text{NO}_2 + 2\text{OH}^{-} \rightarrow \text{NO}_2^{-} + \text{NO}_3^{-} + \text{H}_2\text{O}$
$\text{Let's find the oxidation state of Nitrogen in each compound:}$
$\text{In } \text{NO}_2\text{, let O.S. of N be } x\text{. } x + 2(-2) = 0 \Rightarrow x = +4\text{.}$
$\text{In } \text{NO}_2^{-}\text{, let O.S. of N be } y\text{. } y + 2(-2) = -1 \Rightarrow y = +3\text{.}$
$\text{In } \text{NO}_3^{-}\text{, let O.S. of N be } z\text{. } z + 3(-2) = -1 \Rightarrow z = +5\text{.}$
$\text{In this reaction, nitrogen in } \text{NO}_2 \text{ (oxidation state } +4 \text{) is converted to nitrogen in } \text{NO}_2^{-} \text{ (oxidation state } +3 \text{), which is a reduction.}$
$\text{Nitrogen in } \text{NO}_2 \text{ (oxidation state } +4 \text{) is also converted to nitrogen in } \text{NO}_3^{-} \text{ (oxidation state } +5 \text{), which is an oxidation.}$
$\text{Since the same element, Nitrogen, is both oxidized (from } +4 \text{ to } +5 \text{) and reduced (from } +4 \text{ to } +3 \text{) in this reaction, it is a disproportionation reaction.}$