The quickest way is to simply read on the Internet what SN can be used for.
Mainly SN is used for curing meat, but this is not the only application.
Once you gain knowledge on this topic, create a reasonable lie.
Alternatively, you can come up with a fictional use for SN.
Of course, provided that your wife has no knowledge about it and is not suspicious.
Above all, be very persuasive.
Don't give evasive answers.
Prepare the entire scenario in your head.