Explain the statement: "$NH_3$ acts as both a Lewis base and a Brønsted-Lowry base,whereas $BF_3$ acts only as a Lewis acid but not as a Brønsted-Lowry acid."

(N/A) $1$. $A$ $Brønsted-Lowry$ base is a proton $(H^+)$ acceptor. $NH_3$ has a lone pair of electrons on the nitrogen atom,which allows it to accept a proton to form the ammonium ion $(NH_4^+)$. Thus,$NH_3 + H^+ \rightarrow NH_4^+$.
$2$. $A$ $Lewis$ base is an electron pair donor. Since $NH_3$ has a lone pair,it can donate this pair to an electron-deficient species,acting as a $Lewis$ base.
$3$. $A$ $Lewis$ acid is an electron pair acceptor. $BF_3$ has an incomplete octet (only $6$ electrons around $B$),making it electron-deficient and capable of accepting an electron pair.
$4$. $A$ $Brønsted-Lowry$ acid is a proton $(H^+)$ donor. $BF_3$ does not contain any hydrogen atoms,so it cannot donate a proton,and therefore,it cannot act as a $Brønsted-Lowry$ acid.