Kangxi Radical Two

No: ⼆ is the radical form; 二 is the ordinary character.

Unicode encoding treats them as separate entries. 二 is the ordinary Han ideograph for the number two and can appear as a word or part of one; ⼆ is a filing symbol. In a dictionary or radical chart, it is radical 7, a label for grouping and finding entries—not the character to use for the number in Chinese text.

The ordinary numeral 二 appears in late-Shang oracle-bone writing around 1200 BCE for quantity and order; bronze inscriptions kept the number sense. ⼆ is the later catalogue form, not an ancient spelling of the number.

How did ⼆ become a dictionary symbol?

It took shape through successive Chinese dictionaries.

The earlier Shuowen Jiezi grouped characters by components. In 1615, scholar Mei Yingzuo’s Zihui dictionary set out a system of 214 radicals plus the strokes remaining in each entry. The Kangxi Dictionary adopted that arrangement in 1716, giving the set its familiar name. The method helps readers find an unfamiliar character by its component and the strokes left over.

Some assignments are filing conventions, not definitions: Unicode's radical index files 井 (the character for a well) under 二. Unicode's Han ordering also consults Chinese, Japanese and Korean reference dictionaries.