I need help answering that middle question

 153

Explanation:

californium is a synthetic radioactive element found on the bottom row of the periodic table, along with other actinides.

It was first discovered in 1950 at the University of California Radiation Laboratory in Berkeley by bombarding curium with alpha particles (helium nuclei). Pure californium metal has a silvery-white appearance and is soft enough to be easily cut with razor blade.

In initial experiments with californium in its concentrated form began in 1958.

Since then, 20 isotopes of californium have been characterize, with mass numbers ranging from 237 to 256. One of these isotopes is californium-252, which was first isolated from a neutron-irradiated sample of plutonium-239. As an exclusively synthetically made element (it cannot be found in nature),

californium-252 is very rare an is produced via neutron bombardment in high flux isotope reactor or particle accelerators.

On this,page we walk through some of the properties  and uses of his unique isotope and provide additional resources for your reference.

Hope this helps! :)

"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."

ill try to . no promises tho.

explanation: