What is the main difference between verification and validation in software…

Verification and validation (V&V) are two complementary quality processes applied throughout the software lifecycle, not two separate lifecycle phases. Verification is the static process of checking that a work product -- requirements, design, or code -- conforms to its specification; it asks 'are we building the product right?' and is carried out through techniques such as reviews, inspections, walkthroughs, and static analysis. Validation is the process of checking that a product (a prototype, an increment, or the finished build) satisfies the user's actual, intended need; it asks 'are we building the right product?' and is carried out primarily through dynamic techniques such as functional testing and user-acceptance testing, though earlier validation activities such as prototype reviews also occur before the build is finished. A foundational principle of testing theory (ISTQB) is that neither verification nor testing can prove the absence of defects -- they can only show that defects are present or that a product does or does not conform to what was specified, never certify total bug-freedom.

Applied to this question, the description that verification checks whether the software is built right while validation checks whether the right software is built matches this standard distinction exactly, and is the definition used across testing references such as ISTQB and standards guidance such as NASA's IV&V documentation.

• Equating verification with a guarantee of bug-free software overstates what conformance-checking establishes: per testing theory, checking conformance to a specification can never certify the total absence of defects -- only their presence, or the product's adherence to what was documented.

• Splitting the two into a strict 'before coding' versus 'after coding' timeline misrepresents both as single, one-time phases; in practice, static verification activities such as reviews and inspections apply throughout the lifecycle (not only before coding), and validation activities such as prototype reviews or early user feedback can begin well before coding is complete.

• Since neither of the above two mischaracterizations holds on its own terms, no combination of them supports a 'more than one correct description' reading, and a correct, standard description of the distinction is present among the choices, so it cannot be that none of them holds either.

This is a BPSC 2024 (Computer Science) previous-year question; BPSC's own official final answer key for this question confirms the same option as correct.