Living things have many characteristics for example we are made up of cells, we use energy and we reproduce
Answer:- 9.4 minutes.
Solution:- Radioactive decay obeys first order reaction kinetics and the equation used to solve this type of problems is:
where, k is decay constant and t is the time. 
is the initial amount of the radioactive substance and N is the remaining amount.
Since the value of decay constant is not given, so we need to calculate it first from given half life by using the formula:
where 
stands for half life.
Given half life is 3.0 minutes.
So, 
Let's plug in the values in the first order reaction equation and solve it for t.
It could also be written as:
k = 9.4 min
So, the radioactive substance would take 9.4 minutes to decay from 40.0 grams to 4.5 grams.
Answer:
Between carbon and silicon, silicon element has the strongest attraction between its nucleus and its valence electrons.
because silicon's nucleus is bigger than carbon.silicon loses electrons easily than carbon.
Reactions can occur because of a precipitation reaction
<h3>Further explanation</h3>
Double-Replacement reactions, happens if there is an ion exchange between two ion compounds in the reactant to form two new ion compounds in the product
To predict whether this reaction can occur or not is one of them, the precipitation reaction. A precipitation reaction occurs if two ionic compounds which are dissolved reacted to produce one of the products of the ion compound does not dissolve. Formation of these precipitating compounds that cause reactions can occur
Chloride solution reacts with Sodium carbonate solution
CaCl₂(aq)+Na₂CO₃(aq)⇒CaCO₃(s)+NaCl(aq)
Because Calcium carbonate, CaCO₃ an insoluble solid , it will precipitates so that a reaction can occur
By changing the number of protons in an element, you are fundamentally changing it to a different element.
It’s worth remembering that:
Protons identify the element
Electrons determine properties and behavior of the element
Neutrons contribute to isotopes and just help keep everything stable, by separating the charges. Remember opposites attract. Like charges repel.
