What is the role of metal or reagents written on arrows in the given chemical reactions?
(a) `{:(CH_(3)),(" \"),(" "C),(" /"),(CH_(3)):}=C{:(" CH"_(3)),("/"),("\"),(" CH"_(3)):}+H_(2) overset(Ni)toCH_(3)-underset(H)underset(|)overset(CH_(3))overset(|)C-underset(H)underset(|)overset(CH_(3))overset(|)C-CH_(3)`
(b) `CH_(3)COOH+CH_(3)CH_(2)OH overset("Conc. "H_(2)SO_(4))to CH_(3)COOC_(2)H_(5)+H_(2)O`
(c ) `CH_(3)CH_(2)OH underset("Heat")overset("Alk. "KMnO_(4))to CH_(3)COOH`

Explanation

To understand the role of metals or reagents written on arrows in the given chemical reactions, let’s analyze each reaction step by step.

### (a) Reaction:
`{:(CH_(3)),(" \"),(" "C),(" /"),(CH_(3)):}=C{:(" CH"_(3)),("/"),("\"),(" CH"_(3)):}+H_(2) overset(Ni)toCH_(3)-underset(H)underset(|)overset(CH_(3))overset(|)C-underset(H)underset(|)overset(CH_(3))overset(|)C-CH_(3)`

**Step 1:** Identify the reactants and products.
- The reactants are alkenes (with a double bond) and the product is an alkane (with single bonds).

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