Step 1: Define the word 'kind'.
The word 'kind' refers to having or showing a friendly, generous, and considerate nature. It implies compassion, gentleness, and benevolence towards others.
Step 2: Evaluate each option for similarity in meaning.
(1) rude: This means offensively impolite or ill-mannered. This is an antonym (opposite) of 'kind'.
(2) merciful: This means showing compassion or forgiveness, especially towards someone who is in one's power. This aligns well with the sense of being compassionate and benevolent, which are facets of being 'kind'.
(3) eager: This means strongly wanting to do or have something. This is unrelated to the meaning of 'kind'.
(4) cruel: This means willfully causing pain or suffering to others, or feeling no concern about it. This is also an antonym (opposite) of 'kind'.
Step 3: Conclude the most similar word.
Among the given options, 'merciful' is the closest in meaning to 'kind' as both convey a sense of compassion and benevolence.
$$(2) merciful$$