Answer:
Oxygen
Explanation:
The electrons present in an atom are arranged in shells or orbitals. The electrons are filled into these shells based on their energy levels with those shells closest to the nucleus filled first as they have the lowest energies.
The arrangement of electrons around the nucleus of an atom is known as electronic configuration. The outermost electron shell of an atom is known as a valence shell shell and the electrons found in this shell are known as valence electrons. The electrons usually exist in pairs. The first shell can only contain two electrons; the second shell can contain 8. the electrons are singly filled first before pairing occurs.
The electronic configuration of the atoms of the elements in the option are as follows:
Helium : 1s² ; valence electrons are 2 which are both paired
Hydrogen: 1s¹ ; valence electron is 1
Oxygen : 1s²2s²2p⁴ ; valence electrons are 6 wit two unpaired electrons
Lithium : 1s²2s¹ ; valence electron is 1
Helium has two valence electrons but they are paired as its 1s shell can only contain a maximum of two electrons.
Oxygen has 6 valence electrons. Two of these electrons are paired <em>while the other two are unpaired.</em>
The answer to the question ; Land ____ is a hazard in which an area of land sinks down due to removal of underground material is letter B. The Subsidence. So we should read it as, The land subsidence is a hazard in which area of land sinks down due to removal of underground material. B, Subsidence.
Active immunity occurs when our own immune system is responsible for protecting us from a pathogen. Passive immunity occurs when we are protected from a pathogen by immunity gained from someone else.
Answer:
The dead matter is the food for microbes which respires and forms carbon dioxide in to the atmosphere. The dead matter is the food for the organism such as saprophytes and decomposers. If the plant or the soil is burnt carbon dioxide is released into the air.As a result some of these particles become soil.
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