Question

an atom that has 54 protons, 54 electrons, and 78 neutrons is _.
\\( _{25}^{54}mn \\)
\\( _{54}^{132}xe \\)
\\( _{54}^{124}xe \\)
\\( _{36}^{84}kr \\)
question 8
1 pts
how many electrons are present in a bromine atom with a mass number of 81?
81
46
24
35

Explanation:

Step1: Identify element by proton number

The number of protons determines the element. The atomic number (Z) is equal to the number of protons. Here, Z = 54. Looking at the periodic - table, the element with atomic number 54 is Xenon (Xe).

Step2: Calculate mass number

The mass number (A) is the sum of protons and neutrons. A=54 + 78=132. So the atom is $\ce{^{132}_{54}Xe}$.

For the second question:

Step1: Recall atomic number of bromine

The atomic number of bromine (Br) is 35. In a neutral atom, the number of electrons is equal to the number of protons, which is equal to the atomic number. So, a neutral bromine atom has 35 electrons regardless of its mass - number.

Answer:

First question: B. $\ce{^{132}_{54}Xe}$
Second question: D. 35