I have seen some options with same strike price only difference being one’s a put and the other’s a call. So as per my basic understanding spot price going up call should go up and put should fall. But i have observed sometimes even though spot is going up, both call and put are decreasing. Any specific reason.
This happens when volatility goes up. Unfortunately no one line answer to explain this. I suggest you to go through options module here and especially on option greeks.
Option Valuations are a big maze - and it is a really complex topic.
There are six different factors that affect an option price. Underlying stock/index price, volatility, time remaining to option expiry, interest rate, strike price of the option, and any possible dividend payouts.
While one factor may go in favour of increasing the option price, the others can bring it down.
To see a basic understanding of how option valuation works, see:
It’s interesting how can there be the same price on different products, especially when the actions are completely different? I think it’s practically impossible, but it’s very easy to check.