C. The number of covalent bonds is equal to the number of unpaired valence electrons. For example, nitrogen and phosphorous both have 3 unpaired valence electrons thus forming 3 covalent bonds.
Answer:
any of two or more forms of a chemical element, having the same number of protons in the nucleus, or the same atomic number, but having different numbers of neutrons in the nucleus, or different atomic weights. There are 275 isotopes of the 81 stable elements, in addition to over 800 radioactive isotopes, and every element has known isotopic forms. Isotopes of a single element possess almost identical properties.
Explanation:
Answer:
Option (A)
Explanation:
The Precambrian represents the time period, right from the beginning of the earth to about 540 million years back. It is divided into 3 parts, namely the Hadean, the Archean and the Proterozoic. Throughout this geological time, vast changes have taken place on earth. The first life forms of about 3.8 billion years old, that existed on earth were the simple unicellular organisms, whose traces were only found at some particular places. These organisms were very small and are comprised of soft bodies, so they were affected by the earth's dynamic processes. The organisms in order to get fossilized must contain hard parts. Due to the presence of soft bodies, the organisms were not fossilized and so it took a long time to demarcate that the late Precambrian organisms were animal-like life.
hence, the correct answer is option (A).
Orchids are now grown through vegetative propagation, rather than seeds, courtesy of developments in cloning. This allows many orchid plants to be grown from a portion of a single orchid plant. This allows even the rare orchid o to be grown in mass. There is also little variation when cloning s done as compared to growing with seeds.
