Identify the transformation

We need to convert butene-1 to butane.

$\text{But-1-ene} = CH_2=CH-CH_2-CH_3$ $\text{Butane} = CH_3-CH_2-CH_2-CH_3$

This conversion means the double bond must be hydrogenated.

Required reaction

Addition of hydrogen across a double bond is done by catalytic hydrogenation:

$CH_2=CH-CH_2-CH_3 + H_2 \xrightarrow{Pd} CH_3-CH_2-CH_2-CH_3$

Check each option

A: $\mathrm{Sn-HCl}$
This is a reducing system, but it is generally used for reducing groups like nitro compounds, not for hydrogenation of an alkene double bond.
Not correct.

B: $\mathrm{Zn-Hg}$
Zinc amalgam is used in Clemmensen reduction (usually with HCl) for reducing carbonyl groups, not alkenes.
Not correct.

C: $\mathrm{Pd/H_2}$
Palladium with hydrogen is a standard catalyst for hydrogenation of alkenes to alkanes.
Correct.

D: $\mathrm{Zn-HCl}$
This is also not used for converting alkenes to alkanes by hydrogenation.
Not correct.

Final answer

The correct reagent is:

$\boxed{\mathrm{Pd/H_2}}$

So, Option C is correct.