Is jealousy portrayed as completely unreasonable? Is there a kind that is reasonable or does all jealousy tend to mock the person who is jealous? Use 2 or more quote from the Merchant of Venice.

One of the more notable quotations about jealousy from this play is one which has since become idiomatic in English. In act 2, scene 3, Portia addresses Bassanio:

How all the other passions fleet to air
As doubtful thoughts, and rash-embraced despair,
And shuddering fear, and green-eyed jealousy!

Portia is saying here that it is very easy for love to turn to doubt and express itself as jealousy. She advises Bassanio, "O love, be moderate." So, Portia does not suggest that jealousy is unreasonable entirely; this quotation seems to indicate that, on the contrary, she thinks it is a completely reasonable and natural first reaction. However, what Portia is suggesting is that jealousy should not be allowed to overcome us entirely. Rather, if we try not to allow ourselves to be made unhinged by jealousy, it can be a force for good.
It can also be argued that jealousy is what drives Shylock to behave as he does towards Antonio and Bassanio, leading, ultimately, to his own downfall. We can certainly see elements of jealousy in what Shylock says in act 1, scene 3. He hates Antonio, "for he is a Christian" but also because "he lends out money gratis and brings down / The rate of usance here with us in Venice." Shylock wants to "feed fat the ancient grudge" he bears against Antonio, partially because Antonio is harming Shylock's moneylending business and partially because he is jealous of Antonio's standing in the society.
However, if Shylock is jealous, we could argue that there is something reasonable in his grudge; he states that Antonio "hates our sacred nation." While Shylock's behavior is not moderate, we cannot blame him for feeling oppressed by the anti-Semitic society in which he lives and which he feels Antonio represents. Indeed, looking back at Portia's comment, we can see how Shylock's "passions" have exhibited themselves as "green-eyed jealousy." Had Shylock used these feelings to power a growth in his business, or otherwise behaved differently in response to them, his jealousy might have become a more positive force. So, arguably, while jealousy destroys in this play, the attitude of the writer is that it is not jealousy itself but how we handle it that is destructive.