Let total number of students in the class be 100.

Indian students = $60\%$ of $100 = 60$

So, foreign students = $100 – 60 = 40$ students

Total number of girls students = $50\%$ of $100 = 50$

According to the question,

Total number of Indian girl students = $30\%$ of $60 = 18$ students

So, foreign girl students = $50 – 18 = 32$

As total foreign students = 40

So, foreign boy students = $40 - 32 = 8$

So, percentage of boys among foreign students = $(\frac{8}{40}) \times 100 = 20\%$

Hence, option (D) is the correct answer.