Answer:
The correct answer would be nonsence mutation.
It is a type of point mutation in which an amino acid coding codon is converted into a stop codon.  
It results in the termination of a premature polypeptide chain.
For example, the mutation of codon third GCT into ACT in which guanine is replaced with adenine.
DNA template strand  3' - TAC TGA GCT GTG GCT CGC TCG ACT - 5'
mRNA sequence         5' - AUG ACU CGA CAC CGA GCG AGC UGA- 3'
Amino acid sequence       Met   Thr    Arg  His    Arg  Ala   Ser    Stop
Mutated DNA template strand  3'-TAC TGA ACT GTG GCT CGC TCG ACT -5'
mRNA sequence                       5'- AUG ACU UGA CAC CGA GCG AGC UGA-3'
Amino acid sequence                   Met   Thr    Stop