Answer: The one day rate of return on the stock is 1.49%
We arrive at the answer in the following manner:
First we need to calculate yesterday's and today's index values. 
For that we need to find weights of each day based on market capitalization.

The weight of a company in the index is calculated by dividing the market capitalization  of a company by the total market capitalization of all the companies whose shares are a part of the index.

Then, we multiply the share price of each company with their respective weights and find the total to arrive at the index value for one day.
<u>Yesterday's Index Value</u>
Stock        Price         No. of shares      Mkt Cap  Weight  Weight*Price
A               12               600000        7200000      0.25      2.96 (0.25*12)    
B               20               500000       10000000    0.34      6.85(0.34*20)
C               60               200000       <u>12000000</u>     <u>0.41</u>      <u>24.66  </u>(0.41*60)
Total                                                 29200000     1.00      34.47
We calculate the weight for stock A as follows:

We calculate the weights of the remaining stocks in a similar manner.
Please note that the sum total of all weights must add up to 1.
The sum total of the last column (Price * Weight) is yesterday's index value.
We repeat the same steps with today's market price to arrive at today's index value.
<u>Today's index Value</u>
Stock        Price   No. of shares       Mkt Cap     Weight    Weight*Price
A               16               600000       96,00,000     0.31        4.95 (0.31*16)    
B               18               500000       90,00,000     0.29       5.23  (0.29*18)
C               62               200000    <u>1,24,00,000</u>     <u>0.40</u>     <u>24.80</u>(0.40*62)
Total                                                3,10,00,000     1.00     34.98
<u>One-day Rate of Return</u>
We can calculate the one day rate of return on the index as follows:



Rate of return = 0.01494 or 1.49%