Q.Who disproved Lamarck's theory of Acquired characters ? How ?

The idea that the use and disuse of organs drives evolution was proposed by Jean-Baptiste Lamarck, not by Darwin, Malthus, or De Vries.

Jean-Baptiste Lamarck proposed the theory of inheritance of acquired characteristics.

Lamarck's theory of inheritance of acquired characters (1809), also called Lamarckism, states that organisms develop new structures or modify existing organs in response to a need created by their environment, and that such use-and-disuse based changes acquired during an organism's lifetime are passed on to its offspring. His classic illustration was the giraffe stretching its neck to reach leaves on tall trees, which he believed led to progressively longer necks i …

Jean-Baptiste Lamarck proposed that organs used repeatedly during an organism's lifetime become better developed and this acquired improvement is inherited by the next generation.

Jean-Baptiste Lamarck (1744-1829) put forward the theory of inheritance of acquired characters (also called Lamarckism, or the theory of 'use and disuse'). He proposed that body parts/organs that are used extensively become stronger and more developed over an organism's lifetime, while unused organs gradually degenerate, and that these acquired changes are passed on to the offspring. His classic (though now scientifically discredited) example was the giraffe's long neck, which he explained as resulting from ancestors continually stretching their necks to reach …

Lamarck proposed the theory of inheritance of acquired characters.

Jean-Baptiste Lamarck's theory (Lamarckism) held that characters an organism acquires in its lifetime — for example through use and disuse of organs, like the supposed lengthening of the giraffe's neck — are inherited by its offspring. It was later refuted by Weismann's germ-plasm work and by genetics, but it is historically important in NCERT Class 12 Biology evolution.

…

Lamarckism proposed that characters acquired by an individual during its life, through the use and disuse of organs, are inherited by its offspring.

Jean-Baptiste Lamarck (1744–1829) proposed the theory of inheritance of acquired characters, also called Lamarckism, based on two main principles: (1) use and disuse of organs — organs that are used extensively become stronger and more developed, while those not used degenerate over generations (e.g., the long neck of giraffes was explained as resulting from generations of stretching to reach high foliage); and (2) these acquired changes are then transmitted to the offspring.

…