Answer:
Ionic solids
Explanation: Ionic solids—Made up of positive and negative ions and held together by electrostatic attractions. They're characterized by very high melting points and brittleness and are poor conductors in the solid state. An example of an ionic solid is table salt, NaCl.
Answer: No
Explanation:
A periodic table can be defined as the table in which the row of chemical elements are present. All the elements of the row have same number of electron shells.
The arrangement of elements is based on atomic numbers, electron shell model and other chemical properties. The elements are placed in increasing order of atomic number.
This table does not give information about the occurrence of the elements.
Answer:
through natural selection
Explanation:
Natural selection is the driving mechanism of the evolution of species. Organisms can survive more in an environment if they are capable to adapt the changing environmental conditions. After surviving they are also able to pass their modified trait into their future generations (evolution).
Helpful variations accumulate through natural selection, as the organisms that are better adapted to their environment reproduce offspring with the same variations.
Answer:
D. Z, X, Y
Explanation:
Step 1: Z
Within the Sun two protons fuse together and when this proton-proton pair breaks apart one proton transform into neutron due to weak nuclear force. Along with transformation of neutron, a positron also formed and proton-neutron pair sometimes form deuterium.
Step 2: X
Collision of third proton takes place with deuterium and this collision results in formation of Helium-3 along with gamma rays. These gamma rays are also released as sunlight.
Step 3: Y
Collision of two Helium-3 nuclei takes place which results in creation of Helium-4.
