b. They contain younger stars and more gas and dust.
c. They are bigger than spiral galaxies.
d. They are smaller than spiral galaxies.
Answer:
A. They contain older stars and less gas and dust.
Explanation:
There are three types of galaxies:
Elliptical galaxies are galaxies shaped like an ellipse, while spiral galaxies consist of a flat, rotating disk that contains stars, gas, and dust, and a central concentration of stars called the bulge.
The difference between elliptical and spiral galaxies is in the amount of gas and dust they contain. Spiral galaxies contain large amounts of gas and dust, which means that new stars are born very often. This makes them brighter than relatively dim elliptical galaxies, which contain less gas and dust. This is why fewer new and brighter stars are born in elliptical galaxies, leaving them with older, dimmer stars.
Answer:
the same number of electrons in their outermost shells
Explanation:
On the periodic table, elements in the same column have the same number of electrons in their outermost shells (also known as valence electrons), and hence, are said to belong to the same group.
Similarly, elements on the same row in the periodic table have the same number of atomic orbitals and are said to belong to the same period.
The elements in each column have the same number of electrons in their outermost shells.
Elements are defined as the substances in chemistry that can not be broken down by any further chemical reaction.
Typical examples of elements include: oxygen, hydrogen,Helium, calcium, potassium, iron, Chlorine.
These elements are arranged in columns and the rows of the periodic table according to their atomic numbers.
The elements in each column have the same number of electrons in their outermost shells.
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B
It changes direction when it passes through an opening
С
It changes its speed and wavelength when it passes through an opening
D
It changes direction when it passes from one medium to another
E
It changes its speed and wavelength from one medium to another.
F
It changes direction when it bounces off of a solid surface.
If a sound wave refracts,It changes its speed and wavelength when it bounces off of a solid surface,It changes its speed and wavelength when it passes through an opening, and It changes direction when it passes from one medium to another. Therefore, option A, C and D are correct.
An important case in which sound waves change form or spread out is called refraction. This phenomenon affects the bending of a sound wave owing to changes in the wave's speed.
Refraction is the reason ocean waves near a shore parallel to the beach and why glass lenses can be used to focus light waves.
If the air above the earth is warmed than that at the surface, sound will be change shape back downward toward the surface by refraction. Soundpropagates in all directions from a point source.
Thus, option A, C and D are correct.
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b. conduction
c. cold air rising and warm air sinking
d. radiation
Answer:
cold air rising and warm air sinking
Explanation:
Convection is well known in nature. During convection, warm particles rise above the surface while cooler particles sink below. Hence a convection current is set up.
Air moves by convection. Hot air rises and moves toward and is then replaced with cooler air. A typical application of convection in nature is land and sea breeze.
b.
At higher elevations, it would take longer to hard boil an egg, because there is a lower boiling point, so the egg is boiling in water at a lower temperature.
c.
At higher elevations, it would take less time to hard boil an egg, because there is a lower boiling point. Therefore it would take less time to achieve the boiling point.
d.
At higher elevations, it would take longer to hard boil an egg, because it would take longer to achieve the boiling point.
Answer:
Se + 2e- => Se-2
Explanation:
Ions are electrically charged particles, formed due to the gain or loss of electrons by an atom.
There are two types of ions cations and anions. An element that loses their electrons and forms positive ions are cations while metals and element that gains one or more electrons and forms negative ions are anions.
Selenium is an atom with atomic number 34 and represented as Se. The electronic configuration of Se is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4. Selenium will gain 2 more electrons to complete it p orbital and form an ion Se-2.
The equation is as below:
Se + 2e- => Se-2