Question

Orthoboric acid when heated to red heat gives

Answer 1

Heating boric (H3BO3) acid at 370 K or above leads to formation of metaboric acid (HBO2). If heating is continued, it further gives boric oxide (B2 O3).

Answer 2

Boric acid on heating above 170C gives metaboric acid, which on further heating above 300C gives tetraboricacid (or boric acid)