Which of the following is a common ground for contesting a will?

Improper execution of the will is a common ground for contesting a will because it pertains to whether the will was created following the legal requirements set forth by the laws governing wills in that jurisdiction. Most jurisdictions require that a will be signed by the testator, and in many cases, must also be witnessed by a certain number of individuals. If a will does not adhere to these formalities, such as missing signatures, lack of proper witness attestation, or failure to comply with other statutory requirements, a court may deem the will invalid.

In contrast, having valid testamentary capacity means that the testator was of sound mind and able to make decisions when creating the will, which is typically not a ground for contesting a will if the capacity is established and supported by evidence. Similarly, witnessing the signing is generally a requirement for valid execution rather than a cause for contesting unless the witnessing was not done correctly. Lastly, the presence of beneficiaries at the time of execution doesn't typically serve as a basis for contesting a will. Their presence has no bearing on the validity of the will itself and is not an issue unless it relates to undue influence or similar concerns.