For 77Se2-, identify each of the followingMass Number

Question

BlackTom AI · Accepted Answer

First, recall what mass number means: A is the total number of protons and neutrons in the nucleus, A = Z + N.

Next, identify the atomic number Z for selenium (Se). Selenium has Z = 34, since there are 34 protons in a neutral selenium atom.

In the given species, 77Se2−, the mass number A is the number shown in front of the element symbol, which is 77. The charge (2−) tells us the ion has two extra electrons, but it does not change the mass number, because mass is dominated by protons and neutrons, and electron mass is negligible in this context.

To verify consistency, compute the neutron count N = A − Z = 77 − 34 = 43. This would mean the isotope is selenium-77 with 34 protons and 43 neutrons, and the 2− charge implies 36 electrons in total? Actually neutral Se would have 34 electrons; Se2− has 36 electrons, confirming the 2− charge.

In summary, the mass number A for 77Se2− is 77, consistent with the notation and independent of the ion’s charge.

For 77Se2-, identify each of the followingMass Number

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