In nostrils, the substance which moistens and keep the incoming air warm is called:

Explanation

When you inhale, the air is first conditioned in the nasal cavity so it reaches the lungs at an appropriate temperature and humidity and free of large particles. The nostrils and nasal cavity have hairs (vibrissae) that block large debris, and the convoluted nasal conchae produce turbulence so air contacts a large, well-vascularized mucous surface. Goblet cells and seromucous glands secrete mucus that humidifies the air and traps particles and microbes; enzymes and IgA in the mucus help neutralize pathogens. The dense capillary plexus in the nasal mucosa transfers heat to the inhaled air, warming it toward body temperature, and cilia move the mucus with trapped debris toward the pharynx to be cleared. Because of these combined features, mucus (from the nasal mucosa) is the primary substance in the nostrils that moistens and helps keep incoming air warm, protecting the delicate lower respiratory tract and optimizing conditions for gas exchange.