Answer:
B) 2
Explanation:
Significant figures : The figures in a number which express the value -the magnitude of a quantity to a specific degree of accuracy is known as significant digits.
The rule apply for the multiplication and division is :
The least number of significant figures in any number of the problem determines the number of significant figures in the answer.
The rule apply for the addition and subtraction is :
The least precise number present after the decimal point determines the number of significant figures in the answer.
(3.478-2.31) = 1.168 ≅ 1.17 (Rounded to least decimal digit)
(4.428-3.56) = 0.868 ≅ 0.87 (Rounded to least decimal digit)
So,
1.17 * 0.87 = 1.0 (Rounded to least significant)
Answer - two significant digits
There’s lots of measurements. (m, kg, s, mol, cm, in, mm) etc

An atom of this isotope contains 5 protons and 10-5=5 neutrons.

The answer is A. 1.67 × 10⁻²⁶ kg.
The most reactive metal on the periodic table is Francium, However, Francium is an artificial element and only minimal quantities have been produced, so for all practical purposes, the most reactive metal available is Cesium, in the alkali metal family.
ANSWER In theory, Francium, in practice the Cesium