Answer:
Density
Explanation:
Density is a measure of how much mass is contained in a given volume
1.) homogeneous mixtures
2.) <span>NaCI, because sodium is a metal and chlorine is a nonmetal</span>
3.) I'm thinking the first the option
Hi , these are the definitions
Chemistry; the science that deals with the composition and properties of substances and various elementary forms of matter.
aquatic system ; ecosystem in a body of water , communities and organisms that are dependent on each other.
depth ; the distance from the top to the bottom of something .
geography ; the study of the earth s physical features and the people ,plants , and animals.
light ; brightness from the sun or from a light.
medium ; between small and large in size.
period ; the name given to a horizontal row of the periodic table.
properties ; attributes of a substance.
refraction ; the change of direction of a ray of light , sound , heat ....
reflection ; reflection is when infrared waves bounce from a surface .
salinity ; a saline substance or a liquid that contains salt.
pressure ; measure of the force applied over an unit area .
photosynthesis ; the process used by plants , algae , and certain bacteria to harness energy from sunlight into chemical energy.
thermocline ; an abrupt temperature gradient in a body of water .
intertidal ; relating to the region between the hide tide mark and the low tide mark .
benthic ; relating to the bottom of a sea or a lake or to the organisms that live there .
pelagic ; relating to or living in the sea far from the shore.
epipelagic ; relating to or inhabiting the uppermost layer of the water column of the open ocean , into which enough sunlight enters for photosynthesis to take place.
mesopelagic ; relating to or inhabiting the layer of the water column in the open sea that lies between the epipelagic and bathypelagic layers at depths of about 200 to 1,000 meters.
bathypelagic ; relating to or inhabiting the layer of the water column of the open sea that lies between the mesopelagic and abyssopelagic layers at depths of about 1,000 to 4,000.
abyssopelagic ; refering to or occurring in the region of deep water above the floor of the ocean .
neritic ; region of water lying directly above the sub littoral zone of the sea bottom .
photic ; pertaining to the generation of light by organisms .
aphotic; zone of an ocean , lowest level at which photosynthesis can take place .
commensalism ; type of a relationship between a plant , an animal , fungus , etc.
competition ; the struggle among organisms .
freshwater systems ; subset of earth s aquatic ecosystems .
marine systems ; inside aquatic system , marine systems include oceans , seas ,etc.
mutual ism ; relation between species of organisms in which both benefit from the association.
organism ; a system with many parts that depends on each other and work together.
parasitism ; the behavior of a parasite .
predation; preying or plundering.
relationships ; the way in which two things are connected .
terrestrial systems ; an ecosystem only found on land forms.
<span />
Explanation:
from the graph study about oxygen content of Earth's atmosphere, we can understand that
1)
4 billions year ago = None, 3 billions year ago = Cyanobacteria and Archaea , 2 and 1 billions year ago = Bacteria and Green algae , 500 Ma = invertebrate fossils started to existence. Early land plants came in to existence around 398 MA that is Devonian. Dinosaurs are came in to existence during Triassic and Jurassic that is around 251 Ma. Man and animals are recent organism came under Holocene that is 11000 years ago.
2)
The first cells on the earth are anaerobic microorganisms, as the CO2 level is too high they survive by using CO2.
3)
Starting around 2.7 billion years ago, photosynthesis by Cyanobacteria and later plants , pumped “OXYGEN” in to the atmosphere. This caused the decline of anaerobic bacteria and allows the diversification of animals as seen in “CAMBRIAN” around 500 millions year ago.
Early vascular plants “CAPTURED” CO2 starting before the Carboniferous period that began around 350 millions year.Leading to lower temperatures and allowing and allowing the seed plants to outcompetes seedless plants.
Modern human activities has raised both “CO2 and METHANE” level in the atmosphere to over leading to higher temperature and extinction of other species.
Answer: 
incorporates both ionic bonding and covalent bonding.
Explanation:
A covalent bond is formed when an element shares its valence electron with another element. This bond is formed between two non metals.
An ionic bond is formed when an element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element and the element which accepts the electrons is known as electronegative element. This bond is formed between a metal and an non-metal.
For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.
Here potassium is having an oxidation state of +1 called as 
cation and nitrate 
is an anion with oxidation state of -1. Thus they combine and their oxidation states are exchanged and written in simplest whole number ratios to give neutral .
is formed by sharing of electrons between two non metals nitrogen and oxygen.
Thus incorporates both ionic bonding and covalent bonding.
