<span>There's a trend in electronegativity. The bottom left of periodic table is the lowest (0.7) and the upper right is the highest (4.0). The most polar is the greatest difference in electronegavity.
hbr- 1~ , hi- 0.5~ ,hcl - 1.3~ , hf-1.8 so,hf is the answer</span>
1. x-ray soft tissue organs - barium
2. reduce pain and fever- acetylsalicylic acid
3. anesthetic- nitrous oxide
4. treat acne - A. benzoyl peroxide
Answer: It is a Lewis acid/base reaction, and 
is the Lewis acid.
Explanation:
According to the Lewis concept, an acid is defined as a substance that accepts electron pairs and base is defined as a substance which donates electron pairs.
can readily accept electrons and thus act as a lewis acid which is short of electrons.
can readily lose electrons and thus act as a lewis base which has excess of electrons.
It is a Lewis acid/base reaction, and is the Lewis acid.
Atomic mass of Br = 79.904
<span>Now lets say y% is abundance of 79Br. </span>
<span>Then abundance of 81Br = (100 - y) </span>
<span>mass due to 79Br = 78.9183 * y/100 = 0.789183y
</span><span>mass due to 81Br = 80.9163 x (100 - y)/100 = 0.809163(100 - y) </span>
<span>Therfore</span>
<span>0.789183y+ 0.809163(100 - y) = 79.904 </span>
<span>0.789183y + 80.9163 - 0.809163y = 79.904 </span>
<span> - 0.01998y= 79.904 - 80.9163
= - 1.0123 </span>
<span>y = 1.0123/0.01998 = 50.67% </span>
<span> 79Br = 50.67% </span>
<span>now
81Br = 100 - 50.67 = 49.33%
hope this helps</span>
