Which of the following can invalidate a will?

The option referring to the failure to observe proper witnessing requirements is indeed correct in the context of invalidating a will. The law mandates specific formalities that must be followed for a will to be considered valid, and witnessing is a critical component of this process. Typically, for a will to be valid, it must be signed by the testator (the person making the will) in the presence of at least two witnesses, who must also sign the will. If these witnessing requirements are not met, the will may be deemed invalid due to lack of proper execution.

In contrast, having multiple copies of a will does not inherently invalidate it, as long as one validly executed original exists. Similarly, revising a will verbally with witnesses present does not hold up legally; changes to a will typically need to be made in writing and executed properly, not merely through oral statements. Drafting a will without legal counsel may lead to mistakes or omissions, but it does not automatically invalidate the will. The validity is primarily hinged on whether the statutory requirements regarding execution and witnessing are met.