Among C₂H₄, H₂O, NH₃, and CH₄, methane (CH₄) has the largest bond angle of 109.5° due to its tetrahedral geometry.
The question asks which molecule has the largest bond angle among C₂H₄, H₂O, NH₃, and CH₄. To solve this, we can look at the molecular geometry and electron-pair repulsion for each molecule. In CH₄ (methane), the molecule has a tetrahedral geometry with four bonding pairs of electrons around the carbon, leading to bond angles of 109.5°. In NH₃ (ammonia), the molecule also has a nearly tetrahedral shape with one lone pair, resulting in slightly less than 109.5° bond angles. H₂O (water) has a bent geometry because of two lone pairs on the oxygen, and its bond angles are even smaller, at 104.5°. C₂H₄ (ethylene), which is not described in detail in the provided information, has trigonal planar geometry around each carbon because of the double bond, with bond angles of approximately 120°.
Considering the molecular geometries, methane (CH₄) has the largest bond angles of 109.5°, which makes it the answer to the question.