To find out how much they will have saved after 10 months, we can follow these steps:

1. Calculate the amount saved per month for each person:

- The man earns \( N150,000 \) per month, and saves 10%:
\[
\text{Savings per month} = 0.10 \times 150,000 = N15,000
\]

- The wife earns \( N125,000 \) per month, and saves 10%:
\[
\text{Savings per month} = 0.10 \times 125,000 = N12,500
\]

2. Calculate the total amount saved per month by both:

\[
\text{Total monthly savings} = 15,000 + 12,500 = N27,500
\]

3. Calculate the total savings over 10 months:

\[
\text{Total savings} = 27,500 \times 10 = N275,000
\]

So, the amount they will have saved after 10 months is:

C. N275,000