Explain how Iago manages to arouse Othello's suspicion in the conversation between Cassio and Desdemona?

How hard it is to convince a rock that it is hard?  Or
water that it is wet?  Or a green-eyed monster that it is green?  Or
monstrous?

In Othello, Iago's plan to
arouse Othello's jealousy is simple and easy.  All he has to do is make an accusation:
Othello will take care of the rest.

So says author and
critic Salman Rushide:

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She [Desdemona] didn't have to be guilty; the
accusation was enough. The attack on her virtue was incompatible with Othello's
honor.

Iago knows that
Othello is paranoid of being thought a cuckold, a man whose wife lays her eggs in other
birds' nests.  It is the worst thing to call a man back then--worse than any racial
epithet.  In this sexist society, it is not difficult to portray women as unfaithful in
a society where men think women are all unfaithful.  It's not difficult to convince a
man of jealousy when his is already jealous.  It's not difficult to convince of husband
that his wife is flirting when the husband is paranoid about it
already.

Here's all Iago has to
say:

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Look to your wife; observe her well with
Cassio;
Wear your eye thus, not jealous nor
secure:
I would not have your free and noble
nature,
Out of self-bounty, be abused; look
to't:
I know our country disposition
well;
In Venice they do let heaven see the
pranks
They dare not show their husbands; their best
conscience
Is not to leave't undone, but keep't
unknown.

Iago's
imagery is clearly visual: "look" and "observe."  Men are arrogant enough to think they
can read women's minds. And the Venetian society is built on distrust of women!  All
Desdemona has to do is laugh at Cassio's jokes, or touch his hand: Othello's jealousy is
inevitable.  The "green-eyed monster" isn't born in Act II or III--it has always been in
Othello and other men of that time too.