Answer:
The probability that a heterozygous mother will give birth to a child with only one copy of the recessive allele is

Explanation:
Let the recessive allele causing lethal disease be represented by "r"
Let the dominant allele causing no lethal disease be represented by "R"
Genotype of heterozygous mother will be

Genotype of heterozygous mother will be

A cross between
and
will produce following offspring




Thus, out of four offspring only child with genotype
will die
Thus, only three offspring remain alive and out of these three only one child with genotype
has one copy of recessive allele.
Thus, the probability that a heterozygous mother will give birth to a child with only one copy of the recessive allele is
