A) Double replacement
Because the reactants switch when they become products
It's the rows. They are periods. (1,2,3,4,5,6,7 - the ones without the letters).
<span><em>Answer:</em>
A strontium-90 atom that has a lost two electrons has <u>38</u> protons, <u>52</u> neutrons, and <u>36</u> electrons.
<em>Explanation:
</em>Atomic number<em> of </em>Strontium (Sr) is 38.
<em>Atomic number = number of protons
</em>Hence, Strontium has 38 protons.
If the element is in neutral state,
number of protons = number of electrons.
Then, neutral Strontium atom should have 38 electrons.
But the question says Sr has lost 2 electrons. Hence, number of electrons should be 38 - 2 = 36.
Mass number = number of protons + number of neutrons.
The given mass number is 90. Hence, number of neutrons should be 90 - 38 = 52.</span>
