A buffer system usually will need a weak acid, like H2CO3, which is carbonic acid, and a strong base, and the only compound that could figure a fairly strong base among the options given is Na2CO3. NH3 and NaHCO3 are weak bases and HF is a strong acid. Therefore the best answer will be letter A
Answer: The concentration of 
will be 
after 416 seconds have passed.
Explanation:
Expression for rate law for first order kinetics is given by:
where,
k = rate constant = 
t = age of sample = ?
a = let initial amount of the reactant = 
a - x = amount left after decay process =
The concentration of will be after 416 seconds have passed.
1. Atoms
2 neutral, proton
3.
Answer:
- C-B
- C-C
- C-N
- C-O
- C-F
Explanation:
As we move along to the <u>right in the same period, the electronegativity</u> and <u>the effective nuclear charge values are higher.</u>
The tendency is that <em>the higher these values are, the shorter the bonds will be</em>.
With that information in mind, and looking at the periodic table, the order would be:
- C-B
- C-C
- C-N
- C-O
- C-F
Where the C-F bond is the shortest among them.
Answer:
C
Explanation:
A physical change is one in which no new substance is formed. The moistening of food by saliva is purely a physical change because no new substance is formed in the process.
A chemical change leads to the formation of a new substance. The action of the enzyme converts starch into sugar which means that a new substance is formed. This is a chemical change.
