1.Hans and Zacharias Janssen created the first microscope.
2.Robert Hooke was the first to use the word “cell.”
3.Anton van Leeuwenhoek observed small organisms he called “animalcules.”
4.Matthias Schleiden theorized that plants are made of cells.
5.Theodor Schwann theorized that animals are made of cells.
6.Rudolf Virchow theorized that cells come from other pre-existing cells.
Answer:
They are all the same = 8
Explanation:
Since the symbol of that atom is not give, we can infer from the given number the nature and kind of element we are dealing with.
The number 15.999 rounded up to 16 is the atomic weight of the atom also called the mass number.
Although not peculiar enough, we are certain that this atom is Oxygen.
On the periodic table, elements are arranged based on their atomic numbers.
Atomic number of oxygen = 8 = number of protons
For every neutral atom on the periodic table, the number of protons and electrons are the same
Atomic number of oxygen = number of protons = number of electrons = 8
Number of neutrons = Mass number - atomic number = 16 - 8 = 8
A single replacement or displacement reaction occurs when one ingredient in a compound replaces another. Only another metal can replace a less active one; a metal can only displace another metal, and a non-metal can only displace another non-metal.
<h3>Displacement reaction:</h3>
The tendency of the element to lose electrons is what makes it metallic. Due to their bigger sizes and propensity to lose electrons as size, the number of shells, and nuclear force of attraction rise, the most active metals are found on the left side of the periodic table.
The reaction in which the more reactive element displaces the less reactive element is known as the displacement reaction.
When we combine an active metal with HCl, the reaction is as follows:
We are taking sodium, Na which is the most active metal. It will replace H in HCl because it is more reactive than H.
2Na + 2HCl → 2NaCl + H₂
Three ways to recognize if a single displacement reaction has taken place:
1. Color change
2. Formation of bubbles (a gas)
3. Formation of a precipitate
Learn more about displacement reaction here:
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Answer: Wind current
Explanation:
The wind current is the main driving force along with the water currents when one reaches to the seashore. The wind currents above surface of water generates due to the evaporation of water.
The strong wind currents can pull any animal or human walking or running near the sea shore. These currents bring the animal or human towards the sea.
<h2>
Answer:</h2>
Option B. Potassium(K).
<h2>
Explanation:</h2>
Electronic configuration of the given elements are:
- Ca - [Ar] 4s²
- K - [Ar] 4s¹
- B - [He] 2s2 2p1
- Kr - [Ar] 3d¹⁰4s²4p⁶
- Krypton(K) have 36 electrons and it is a noble gas and hence all of its shells are completely filled with electrons and hence it will never loose electrons in normal conditions.
- Boron(B) have 5 electrons and 3 electrons in its outer shell. In order to attain a stable configuration it will loose 3 electrons and it is difficult to loose 3 electrons at a time for an atom.
- Calcium(Ca) have 20 electrons and 2 electrons in its outermost shell, in order to attain a stable configuration it will loose 2 electrons. it is quite difficult but easier than Boron.
- Potassium(K) have 21 electrons and 1 electron in its outermost orbit and in order to attain a stable configuration it will loose 1 electron. It is much easier to donate 1 electron than 2 or 3 electrons.
Result: Potassium will loose an electron most easily from the given elements.
