Answer:
21
Explanation:
Formula;
Mass number = number of protons + number of neutrons
= 9 + 12
= 21
It will be K-potassium because when you go down a group the electronegativty gets bigger while when you go across the period they get smaller because of the valence electrons. Group 8 has the lowest electronegativty because they have a full outer shell. From left to right on the periodic table it decreases but from top to bottom it increases.
Gravity. The rock is being pushed down and you are counteracting that force with a crowbar pushing it upward.
Ferns reproduce with spores which existed the longest in Earth history.
Gymnosperms reproduce with cones and has needle-like, waxy leaves.
Angiosperms reproduce with flowers and newest type of plant in Earth history.
<h3>How ferns, gymnosperm and angiosperm reproduce?</h3>
Ferns reproduce with spores that existed the longest in Earth, gymnosperms reproduce through the formation of cones having needle-like, waxy leaves whereas angiosperms reproduce with flowers which turns into seed. The newest type of plant in Earth history is also belongs to this group.
Learn more about spore here: brainly.com/question/1022692
<span>Quantum mechanic model is based on mathematics. As per this theory the exact position and momentum of electron is impossible to understand. It uses complex shapes of orbitals called electron clouds. n describes the energy of an electron. Larger the value of n larger the distance of electron from the nucleus and larger the orbital. l describles the shape of orbital. Orbitals having same of value of n and different values for l are called subshells.</span>
