Which gas makes up approximately 21 percent of Earth's atmosphere and is essential for respiration?

Which type of lens is used to correct myopia or nearsightedness?

Which everyday device uses the principle of capillary action to function?

Which scientist developed the process of pasteurization and contributed significantly to the germ theory of disease?

Which scientist is credited with developing the first successful smallpox vaccine?

Which type of immunity is gained through vaccination by introducing a weakened or inactivated pathogen?