Lord Vishnu holds a Disc (Chakra), Conch (Sankha), Komidi Gadha, and also holds other elements like a lotus in his hand.
Is there any explanation in scriptures of why Lord Vishnu holds these particular weapons?
Lord Vishnu carries all the tattvas in the world in the form of his weapons. Each weapon and ornament is a symbolism for each tattva.
The symbolism and significance of them are described in 7 verses in Vishnu Purana Chapter 22:
The glorious Hari wears the pure soul of the world, undefiled, and void of qualities, as the Kaustubha gem. The chief principle of things (Pradhána) is seated on the eternal, as the Srivatsa mark. Intellect abides in Mádhava, in the form of his mace. The lord (Íśwara) supports egotism (Ahankára) in its twofold division, into elements and organs of sense, in the emblems of his conch-shell and his bow. In his hand Vishńu holds, in the form of his discus, the mind, whose thoughts (like the weapon) fly swifter than the winds. The necklace of the deity Vaijayantí, composed of five precious gems, is the aggregate of the five elemental rudiments. Janárddana bears, in his numerous shafts, the faculties both of action and of perception. The bright sword of Achyuta is holy wisdom, concealed at some seasons in the scabbard of ignorance. In this manner soul, nature, intellect, egotism, the elements, the senses, mind, ignorance, and wisdom, are all assembled in the person of Hrishikeśa. Hari, in a delusive form, embodies the shapeless elements of the world, as his weapons and his ornaments, for the salvation of mankind.
So, each weapon or ornament corresponds to a tattva.