Question

What characteristics do mutations have?

Answer 1

All have some validity, except "always harmful". Of the remaining choices, "occasionally beneficial" is the best (and it disproves "always harmful", but the common, unlisted "no impact" also does).

The others can describe some mutations, but are not qualified by "occasionally", "sometimes" or some other indication of non-universality:
omission of information -- lost bases or sequences
addition of information -- inserted bases or sequences
mistakes in copying -- sometimes the gene is damaged when replication is not in progress