Boric acid is an acidic molecule because its molecule;
A] accepts $OH^-$ from water releasing proton
B] combines with proton from water molecule
C] contains replaceable $H^+$ ion
D] gives up proton

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Hint: Boron belongs to p-block and is the first member of its group. Boric acid has a formula of $B[OH]_3$. It is also known as orthoboric acid. It is monobasic Lewis acid. Oxygen gives one electron to boron, so it acquires a positive charge and becomes unstable, so it furnishes $1H^+$ and gets stable.

Complete answer:
A] As boron is small in size and boron has 5 electrons in its valence shell. It accepts $OH^-$ from the water molecule and loses its proton.
\[\]$B\mathop {\left( {OH} \right)}\nolimits_3 + \mathop H\nolimits_2 O \to \left\{ {B\mathop {\left[ {OH} \right]}\nolimits_4 } \right\} + \mathop H\nolimits^ + $
Hence this option is correct
B] It does not combine with a proton to form a water molecule rather it loses its proton too. so, this option is completely wrong
C] The acids are also those which contains replaceable hydrogen ion as HCl but not boric acid and hence this option also goes wrong
D] The compounds which give up proton are called Bronsted Acid for example nitric acid. so, this option is also wrong.
Our required Ans is ‘A’ that is accepts $OH^-$ ion from water and gives proton.

Orthoboric acid or boric acid is white, needle-like crystals and have a soapy touch
It is prepared by treating concentrated sulphuric acid with borax.
On heating to high temp say 373K it gives metabolic acid.
It is used in antiseptics, in the manufacturing of enamels, food preservatives,s and in the glass industry.