Answer:
In both nuclear and chemical reactions, two physical quantities are seen to be conserved and unchanging: the number of particles and the total charge. A constant number of particles in nuclear reactions does not imply that mass is conserved.
Explanation:
The given question is incomplete. The complete question is:
A brick has a mass of 4.0 kg and the earth has a mass of 
Use this information to answer the questions below. Be sure your answers have the correct number of significant digits. What is the mass of 1 mole of bricks? Round your answer to 2 significant digits. How many moles of bricks have a mass equal to the mass of the Earth? Round your answer to 2 significant digits.
Answer: The mass of 1 mole of bricks is 
2.5 moles of bricks have a mass equal to the mass of the Earth
Explanation:
According to avogadro's law, 1 mole of every substance weighs equal to its molecular mass and contains avogadro's number 
of particles.
Mass of 1 brick = 4.0 kg = 4000 g (1kg=1000g)
Thus mass of 1 mole of brick or bricks will be = 
The mass of 1 mole of bricks is
Now will correspond to = 1 mole of bricks
will correspond to =
2.5 moles of bricks have a mass equal to the mass of the Earth
2H2 + O2 = 2H2O since two elements created a compound, in this case water.
<h3>Answer:</h3>
The reactivity of an alkali metal depends on the metals ability to <u>loose an electron</u>.
<h3>Explanation:</h3>
Alkali metals are elements present in first group of the periodic table. Following are the metals from top to bottom;
Lithium
Sodium
Potassium
Rubidium
Cesium
Francium
These s-block elements are considered the most reactive metals in the periodic table because they have only one electron in their valence shell and readily loose that electron to form an ionic bond with non metal. The general electronic configuration of these metals is as follow,
nS¹
Also, the reactivity of these metals increases from top to bottom in the group as the ionization energy decreases due to increase in shielding effect respectively.
