When chaos sourcerer is summoned can you fiendish chain it to negate effect or the turn player has priority activate effect?

You cannot Fiendish Chain a Chaos Sorcerer when it's summoned. Here's why:

* Fiendish Chain's effect: Fiendish Chain negates the effects of a monster on the field. It doesn't stop monsters from being summoned.

* Summoning vs. Effect activation: Summoning a monster is a separate action from activating its effects.

* Priority: When a monster is summoned, the player who summoned it gets priority to activate effects (if any) before the opponent.

In summary: When Chaos Sorcerer is summoned, you cannot use Fiendish Chain to negate its summoning effect. You can only use Fiendish Chain to negate its effects after it's on the field and has activated an effect.