Explanation

The drum of a Photostat machine (also known as a xerox machine) is made of a material called selenium,

That is a photoconductive element.

This means that when exposed to light

It becomes conductive, allowing the machine to transfer the image onto the paper. 

Explanation

Potassium is the chemical element 

symbol K 

atomic number 19

Electron configuration: 4s1

Electrons per shell: 2, 8, 8, 1

Explanation

The cell is the smallest unit of life

The atom is the smallest and most fundamental unit of matter.

It consists of a nucleus surrounded by electrons.

Explanation

Hypocenter is the point beneath the Earth’s surface where the vibrations of an earthquake originates and which corresponds to the location where the motion on a fault surface starts.

Explanation

Solder is an alloy of  Lead and tin  

An alloy is a mixture of chemical elements of which at least one is a metal. 

Explanation

Tritium is an isotope of hydrogen that is composed of one proton, two neutrons, and one electron.

The symbol for tritium is 3^H.

The atomic number of tritium is 1 

the atomic mass of tritium is 3.

Explanation

Lead is the metal that pollutes the air of big cities.

Due to the usage of lead petroleum,

when a lead is emitted, it causes damage to air and is a major pollutant.

Explanation

The density of ice is 0.9168 g/cm 3.

The density of water is 1 g/cm 3

Explanation

Cadmium rods are inserted in nuclear reacter to absorb the extra nucleons.

Cadmium has a high thermal neutron absorption cross section.

Therefore, cadmium rods will absorb neutrons, making them unavailable to cause fission.

**** 

Explanation

Photon with energy greater than 1.02 MeV can interact with matter as Pair Production.

MeV stands for Mega electron-volt.

****