(B) Percentage
Net attendance ratio is expressed as a percentage of total children in the age group of 6–10 years attending school.
The term "net attendance ratio" measures the proportion of children in a specific age group attending school, and proportions used for such comparisons are always expressed as percentages. Examiners expect students to distinguish between ratio, percentage, fraction, and index — "percentage" is the standard term used in this context in the NCERT Economics textbook.