<prompt> By which route of administration , least onset of action will be produced from the given options ?Application to a serous surfaceInhalation of gaseous formApplication to a bronchotracheal mucous membraneInjection into blood vessels  <response>: Routes of Administration: In order of rapidity of action: 1 Inhaled in gaseous or vapourous form. It usually involves a volatile substance, gas, dust, smoke or aerosol. 2 Injection into blood vessels. 3 Intramuscular, subcutaneous and intradermal injection. 4 Application to a wound. 5 Application to a serous surface. 6 Application to a bronchotracheal mucous membrane. 7 Introduction into stomach. 8 Introduction into the natural orifices, e.g. rectum, vagina, urethra, etc. Some drugs can be given by rectal route to produce a systemic effect, e.g., aspirin, barbiturates, chloral hydrate, chlorpromazine, etc. 9 Application to unbroken skin. Organic phosphates, nicotine, some organic solvents and lewisite gas can penetrate the skin and produce intoxication and death . 