निम्नलिखित में से किस रासायनिक पदार्थ का उपयोग खाद्य परिरक्षक (food preservative) के रूप में नहीं किया जाता है?

To prevent the oxidation and rancidity of potato chips during storage, manufacturers flush the sealed bags with which gas?

Early matches ignited when struck on a rough surface primarily due to the friction of which substance?