Apples turn brown when exposed to air because it undergoes aerial oxidation. Due to this, when the inside of the apple is exposed to the air containing oxygen and water, it turns brown. When apple is uncut, skin of the apple protects it from this process.
If the peeled apple in kept in the refrigerator, the oxidation reaction is greatly slowed down. This is because, rate of chemical reaction decreases with temperature. Hence, in refrigerator it would take several days for it to turn brown.
Carbon Dioxide fire extinguishers extinguish fire by taking away the oxygen element of the fire triangle and also be removing the heat with a very cold discharge. Carbon dioxide can be used on Class B & C fires. They are usually ineffective on Class A fires
They all wear their skeletons on the outside! This is called an exoskeleton and all creatures that have their structure on the outside are included in the phylum of Arthropods.
