When do scientist rely on estimates

The correct answers will be- when the scientists do not not get the expected results in the form of the exact numbers.

Explanation:

Estimation is the process of approximation based on the uncertain or unexpected, unstable and incomplete data.

The process of estimation is sometimes followed by the scientists like when predicting the exact age of the Earth or the evolutionary facts of species which is impossible to predict and the data does not provide the exact numbers.

Thus, scientist relies on estimated when they do not get the expected results in the form of exact numbers.

atomic number of carbon is 6

electronic configuration of carbon is 1s²2s²2p²

orbital diagram of carbon is as shown here in the image.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."