Questions

Troposphere is the most densest layer and is the lowest atmospheric layer.

Br-Br.

In Br2, two of the same atoms, pull on each side of the bond is equal making it as non-polar.

The other options all include a significantly more electronegative atom (the oxygens and the chlorine), so those bonds are all polar covalent.

In DNA, adenine pairs with Thymine. Similarly, in RNA, due to absence of thymine in RNA and the same structure with uracil helps to pair with adenine.

Epithelial tissue is made of layers of cells that cover the surfaces of the body that come into contact with the exterior world, line internal cavities, and form glands.

The four types of tissue in the body are epithelial, connective, muscle, and nervous. 

The nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body.

In vertebrates it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers or axons, that connect the CNS to every other part of the body.

The nervous system has three main functions:

* To collect sensory input from the body and external environment.

* To process and interpret the sensory input.

* To respond appropriately to the sensory input.

A clade is a group of ancestral species and all its descendants. Hence it is a branch of one same species and so monophyletic.