Is there any limit for the number of lots we can buy in stock Options?
There is Quantity Freeze set by Exchange, you can buy only that many quantities in one order, you can download the Quantity Freeze file from here, the list contains Quantity Freeze limits for all F&O scrips.
Along with this there is OI Limit set by exchange per individual. It is set at 5% of Total Open Interest as explained here.
Thanks. So this limit is only for one order right? I can buy small small quantities and there is no limit for that?
Yes, limit is only for one order.