Answer: Option (b) is the correct answer.
Explanation:
A covalent bond is defined as the bond which occurs due to sharing of electrons between the combining atoms.
Generally, a covalent bond is formed between non-metals.
For example, both nitrogen and oxygen atoms are non-metals and they combine covalently to form 
compound.
As nitrogen has 5 valence electrons and an oxygen atom has 6 valence electrons. So, there occurs unequal sharing of electrons between the two.
Thus, we can conclude that when a covalent bond forms then electrons in valence shells are shared between atoms.
Answer:
The mass percent of potassium is 39%
Option C is correct
Explanation:
Step 1: Data given
Atomic mass of K = 39.10 g/mol
Atomic mass of H = 1.01 g/mol
Atomic mass of C = 12.01 g/mol
Atomic mass of O = 16.0 g/mol
Step 2: Calculate molar mass of KHCO3
Molar mass KHCO3 = 39.10 + 12.01 + 1.01 + 3*16.0
Molar mass KHCO3 = 100.12 g/mol
Step 3: Calculate mass percent of potassium (K)
%K = (atomic mass of K / molar mass of KHCO3) * 100%
%K = (39.10 / 100.12) * 100%
%K = 39.05 %
The mass percent of potassium is 39%
Option C is correct
For example, certain medications may influence the results of the test.
Drug test can show the presence of illicit or prescription drugs on hair samples, although the person has not used these drugs.
Some of false positive drug use is because of this medications: antihistamines, decongestants, antibiotics, antidepressants, analgesics and antipsychotics.
D milk turning sour
the other options are physical changes
