Calculation:
To find the per capita income of India in 1977-78 at 1970-71 prices, we need to use the following formula:
Per Capita Income = National Income / Total Population
Given:
The per capita income of India in 1977-78 at 1970-71 prices is to be determined.

To find the per capita income, we need to know the national income and the total population of India in 1977-78 at 1970-71 prices.
Unfortunately, the given information does not provide the national income or the total population. Therefore, we cannot calculate the exact per capita income.
However, we can make an educated guess based on the options provided.
Looking at the options:
A. Rs. 590
B. Rs. 690
C. Rs. 790
D. Rs. 890
We can see that option B, Rs. 690, is the most reasonable choice as it falls within a reasonable range for per capita income in that time period.
Therefore, the per capita income of India in 1977-78 at 1970-71 prices can be estimated to be Rs. 690.
Note: It is important to note that without the exact data for national income and total population, we cannot determine the exact per capita income. The given answer is an estimation based on the options provided.