Questions

The mesosphere lies above the stratosphere and extends to an altitude of about 85 km. This is layer is often referred to as the cold layer, as the lowest readings in the atmosphere are found here.

Temperature decreases with height, reaching a minimum average value of -90 ºC at the top of the layer.

An invention that improved safety for railway passengers is Air brakes. With the use of air brakes using compressed air, become more effective by preventing many train accidents.

A mixture is made from different substances that are not chemically joined.Compound:

•Two or more elements combine together chemically to form a new substance called compound.

•The different elements are chemically joined together.•Compounds are homogeneous, i.e. their properties are the same throughout

•The compound has properties different from the elements it contains.

•It can only be separated into its elements using chemical reactions. (not using physical methods)

•During the formation of a compound from its elements, a certain amount of energy in the form of heat, light, electricity is either absorbed or evolved

Synapsis is the pairing of two homologous chromosomes that occurs during meiosis. It allows matching-up of homologous pairs prior to their segregation, and possible chromosomal crossover between them.

Synapsis takes place during prophase I of meiosis.

It is also called as Syndesis.

"National Volunteer Day" & "International Peace Day" are observed on 21st september every year.