Lacking envelope: As indicated by their name, un-enveloped plus-strand RNA viruses lack envelopes and consist only of a nucleic acid core capsid surrounded by protein viruses. Hence, this option is correct
Having DNA: Un-enveloped plus-strand RNA viruses are composed of RNA only. Hence, this option is incorrect.
Act indirectly: Un-enveloped plus-strand RNA viruses act directly as mRNA after infecting a host cell, attaching to the host's ribosomes and being translated.That's why they are called "plus strand viruses". Hence, this option is incorrect.
Enveloped: Un-enveloped plus-strand RNA viruses lack envelopes and consist only of a nucleic acid core capsid surrounded by protein viruses. Hence, this option is incorrect.
Lacking envelope: As indicated by their name, un-enveloped plus-strand RNA viruses lack envelopes and consist only of a nucleic acid core capsid surrounded by protein viruses. Hence, this option is correct